Pool Chemistry Field Guide

Effect & benefit: Keeps free chlorine at the CYA-indexed target (§1.4). That kills bacteria and viruses, oxidizes sweat and urine, and keeps algae from starting. Unlike tablets or cal-hypo, it adds no CYA and no calcium, so nothing creeps up over the season except salt.

How to use:

1. Test FC (and CYA monthly so you know the target).
2. Calculate the dose: (target FC − current FC) × amount per +1 ppm from the dose card.
3. With the pump running, pour slowly into the deep end in front of a return, or along the wall away from vinyl seams. Keep the jug low to avoid splashing.
4. Dose in the evening if you can. An evening dose isn't eaten by sun before it circulates.
5. Retest next day. Your daily loss tells you the routine dose.
6. SWG pools: use this when the cell is down, in water too cold for the cell, or to catch up after heavy use.

How much (per 10,000 gal) · basis: stoichiometry

Outdoor pools with CYA 30–50 typically lose 1–4 ppm a day in summer sun. Use your own measured loss, not this range.

Cautions:

• The jug weakens in heat and with age. Dose by test result, not by habit.
• Every ppm adds ~1.65 ppm salt, plus chlorate as it ages. Long-running bleach pools reach 1,000–2,000 ppm salt, which is harmless.
• Don't pour it into the skimmer right after acid.
• Never pour concentrate straight onto a vinyl liner.

Effect & benefit: A one-time high dose. It burns off combined chlorine (chloramines), body oils, and other organic load after heavy use, a storm, or an opening. The water clears and the "chlorine smell" goes away.

How to use:

1. Brush walls and floor, empty the baskets, and make sure the filter is clean.
2. Pump on. Add the dose in the evening, poured slowly in front of a return.
3. Keep the pump running at least 8 h.
4. Retest FC and CC next morning. If CC is still > 0.5, the shock wasn't strong enough — use O1 SLAM.
5. Re-enter only when FC is back down to your label's swimming limit.

How much (per 10,000 gal) · basis: label + stoichiometry

Typical labels say to add enough "to yield 5 to 10 ppm":

Exact amounts for a measured rise:

Cautions: Fixed "1 gallon per 10,000 gallons" directions ignore CYA. At CYA 60+, a 10 ppm shock is weak (use §1.4). At CYA 0 it's very strong. Bromine pools: chlorine shock is also the oxidizer that turns bromide back into bromine (see O3).

Effect & benefit: Kills suspended and wall algae: green, yellow/mustard, and the surface layer of black algae. Labels for visible algae call for multiples of the shock dose.

How to use:

1. Brush every surface hard.
2. Add the algae dose.
3. Run the pump 24 h a day and brush again daily.
4. Vacuum dead algae (to waste if it's heavy), then clean the filter.
5. Keep FC up until the water is clear and stays clear overnight.

How much (per 10,000 gal) · basis: label + stoichiometry

Labels call for roughly double the shock dose when algae is visible. HTH's guidance is 2 gal of 10% per 10,000 gal for severe algae, about +20 ppm.

Cautions: One big dose often only knocks algae back. Holding the right level until three tests pass is what kills it, and that's SLAM (O1). Very high FC bleaches the pH indicator (§1.7).

Effect & benefit: The Trouble Free Pool method for algae, cloudy water, persistent CC, and pool openings. You set FC from CYA (40% of CYA) and hold it there, re-dosing through the day, until three objective tests pass. This kills algae completely instead of knocking it back, and the tests tell you exactly when you're done.

How to use:

1. Test CYA (it sets the target) and pH. Lowering pH to ~7.2 at the start makes chlorine work a little faster.
2. Brush the whole pool, clean the filter, and run the pump 24/7 throughout. Turn the SWG off or down and dose by hand.
3. Raise FC to the SLAM level in the table below.
4. Test every few hours while awake. Re-dose back to the SLAM level each time it drops. Brush at least daily.
5. Continue until all three pass:
   • CC ≤ 0.5 ppm
   • the overnight loss test (O2) loses ≤ 1 ppm
   • the water is clear (the main-drain grate is crisp)
6. Then stop dosing and let FC fall back to its normal target.

How much — reaching the SLAM level from FC 0 (per 10,000 gal) · basis: stoichiometry (targets: TFP chart)

Mustard (yellow) algae (Trouble Free Pool method):

1. First pass a normal SLAM: all three exit tests, CC ≤ 0.5, overnight loss ≤ 1 ppm, and clear water.
2. Raise FC to the mustard level, ≈ 60% of CYA, and hold it for 24 hours.
3. At the same time, sanitize every swimsuit, toy, float, brush, and vacuum head that touched the water (O5). Mustard algae reinfects from them.

Cautions:

• FIFRA: SLAM levels can exceed a label's shock dose and re-entry limit. Follow your label for swimming.
• Above CYA ~80, SLAM gets expensive. A partial drain to lower CYA first is often cheaper.
• At these levels, read pH only after neutralizing the sample (§1.7).
• Pour slowly near returns to avoid bleaching vinyl.

Effect & benefit: A free diagnostic for algae or organic load you can't see yet. With no sunlight, clean water loses almost no chlorine overnight. A loss above 1 ppm means something is still consuming it. It's also the second of SLAM's three exit tests.

How to use:

1. Make sure FC is at least at your normal target. Turn the SWG off for the night, and add nothing overnight.
2. Test FC after the sun is fully off the water. Use a 25 mL FAS-DPD sample, which reads to 0.2 ppm.
3. Test again just before sunrise, the same way.
4. A loss of ≤ 1 ppm passes. More than 1 ppm fails: something is still consuming chlorine (algae, organics, a dirty filter). SLAM, or keep SLAMming.

How much (per 10,000 gal) · basis: stoichiometry

There's no special dose. Just be at or above target, using the dose card above. As a reference, a 1 ppm loss in 10,000 gal equals 12.8 fl oz of 10% (10.2 fl oz of 12.5%) chlorine consumed overnight.

Cautions:

• A cover doesn't change the result; just do it the same way every time.
• Test-strip or color-block precision isn't good enough for this test.

Effect & benefit: Once a bromine pool or spa has a bromide bank (B3), plain liquid chlorine turns spent bromide back into active bromine (HOCl + Br⁻ → HOBr + Cl⁻). This can replace BCDMH tablets entirely. You get no DMH buildup, the cost is lower, and you control the dose exactly.

How to use:

1. Confirm a bromide bank exists: B3 · L1, or an established tablet-fed pool.
2. Test total bromine with a DPD kit; bromine = chlorine-scale reading × 2.25.
3. Add liquid chlorine as below with the pump running. It converts to bromine within minutes.
4. Dose daily or as needed to hold your bromine target.

How much (per 10,000 gal) · basis: stoichiometry (each 1 ppm bromine needs 0.444 ppm FC)

Cautions:

• Label limits: since EPA's 2021 decision on inorganic halides, US sodium-bromide and bromine labels say "not for use in outdoor pools", and outdoor spas must be covered when not in use. Sunlight turns bromine plus bromide into bromate. This method is for indoor pools and covered spas.
• Bromine can't be stabilized, so outdoor sun burns it off quickly.
• Without a bank, chlorine stays chlorine.
• In a 400 gal spa, the +1 ppm dose is only 0.18–0.38 fl oz. Measure with a syringe.

Effect & benefit: Well water often carries dissolved ferrous iron, manganese, or hydrogen sulfide (rotten-egg smell). Chlorine oxidizes them. Iron becomes brown ferric hydroxide, manganese becomes black/brown MnO₂, and sulfide becomes sulfur or sulfate. Doing this on purpose, before the water touches the surface for long, lets you floc or filter the metals out instead of finding them as stains later.

How to use:

1. Test the fill water (or the freshly filled pool) for iron and manganese.
2. Choose a strategy:
   • Keep the metals in solution with a sequestrant (I1). This is simpler and best for low levels.
   • Remove them, as follows. Best for > ~0.5 ppm iron.
3. Raise pH to ~7.6–7.8 and FC to ~10 ppm. The water will turn tea-colored or cloudy brown; manganese is slower and darker.
4. Run the filter 24 h. Then either let the filter catch the precipitate (clean it after), or floc (H3) and vacuum the settled layer to waste.
5. Brush any settled precipitate off plaster promptly, before it stains.
6. Add a sequestrant afterward to hold whatever remains.

How much (per 10,000 gal) · basis: stoichiometry (oxidant demand) + rule of thumb (holding level)

Then hold FC ~10 ppm (1 gal of 10% per 10k gal) until the water clears. Other strengths: multiply the 10% volume by 1.67 (6%), 1.21 (8.25%), or 0.8 (12.5%).

Cautions:

• Precipitated iron stains plaster if it sits. Brush and vacuum the same day.
• If iron is above ~1–2 ppm, a pre-filter or trucked-in water is often cheaper.

Effect & benefit: The same chemical that sanitizes the pool kills mildew and germs on hard surfaces. It also bleaches organic stains on concrete. This is essential after mustard algae, which hides on swimsuits, toys, floats, and brushes and reinfects the pool.

How to use:

1. Clean off dirt first; chlorine is used up by soil.
2. To disinfect: wipe or spray the diluted solution, keep the surface wet ≥ 5 min, then rinse.
3. For gear after mustard algae: submerge brushes, toys, floats, and suits in the pool during a SLAM (O1), or soak them in a bucket of the disinfecting mix for 30 min, then rinse.
4. For mildew on concrete or pavers: wet the plants nearby first, apply the stronger mix, wait 10–15 min, scrub, and rinse well.

How much (per gallon of water, not per pool) · basis: label (CDC/EPA household dilution)

Cautions:

• FIFRA: use a bleach whose label lists surface disinfection when you can.
• Never mix with ammonia or acidic cleaners.
• It bleaches fabrics, cushions, and colored concrete stains — test a small spot first.
• Rinse treated wood and nearby plants.

Effect & benefit: When tap water is unsafe (boil-water notice, no power to boil), EPA's emergency method uses plain household bleach to kill bacteria and viruses in clear water. It's not effective against chemical contamination.

How to use (EPA method):

1. If the water is cloudy, let it settle and filter it through a clean cloth or coffee filter first.
2. Add the drops below, stir, and let it stand 30 minutes.
3. It should have a slight chlorine odor. If not, repeat the dose and wait 15 more minutes.
4. Double the dose if the water is cloudy, colored, or very cold.

How much (per gallon of water) · basis: label (EPA)

Current Clorox bleach is 7.5% (7.1% available chlorine). EPA's table covers 6% and 8.25%, so use the drinking-water directions on the bottle. For 10% and 12.5% pool chlorine, see Cautions.

Cautions:

• Use only plain, unscented bleach with no additives, ideally one whose label gives drinking-water directions.
• Pool "liquid chlorine" isn't labeled for drinking water (FIFRA), and it may carry more chlorate as it ages. Use it only if nothing else exists and the product is certified to NSF/ANSI 60.
  • The same chlorine as EPA's 6% rate is about 5 drops per gallon of 10% or 4 drops per gallon of 12.5%. That's arithmetic, not EPA guidance.
• For well or cistern shock-chlorination, follow your state or county extension procedure.

Effect & benefit: Leaf, berry, acorn, and tannin stains on plaster lighten much faster with concentrated chlorine applied right at the stain than with whole-pool shock. Liquid chlorine is denser than water, so poured slowly from just above the surface, it sinks onto the stain.

How to use:

1. Confirm the stain is organic: it lightens with a trichlor tablet (A5 · O1) and not with vitamin C (I3 · O2).
2. Turn the pump off.
3. Pour liquid chlorine slowly from just above the water directly over the stain. For deep spots, guide it down a length of PVC pipe held over the stain.
4. Wait 15–30 min, brush, then restart the pump.
5. Repeat if needed.

How much (per stain area; counts toward pool FC) · basis: rule of thumb + stoichiometry

Cautions:

• ⛔ Not on vinyl liners: concentrated chlorine bleaches the print.
• Test colored plaster or pebble finishes in an inconspicuous spot first.

Effect & benefit: Every dose in this guide depends on volume, and estimates from dimensions are often 10–30% off. A measured dose of fresh liquid chlorine, read with a precise FC test, gives you the actual gallons. The underlying fact: 1 gal of N% chlorine raises 10,000 gal by N ppm.

How to use:

1. Pass an overnight loss test first (O2). Chlorine demand would make the volume read high.
2. After sunset, with the pump running and the SWG off, test FC with a 25 mL FAS-DPD sample.
3. Add a measured volume of fresh liquid chlorine and circulate 30–60 min. Aim for a rise of 5–10 ppm.
4. Retest FC the same way.
5. Calculate: Volume (gal) = gallons added × strength % × 10,000 ÷ FC rise For example, 1 gal of 10% that raised FC by 6.4 ppm gives 1 × 10 × 10,000 ÷ 6.4 = 15,600 gal.

How much (per 10,000 gal of expected volume) · basis: stoichiometry

Cautions:

• Liquid chlorine loses strength in storage. Old product makes the pool look bigger than it is, so use a fresh jug.
• Repeat on a second night and average the results.

Effect & benefit: A fast, strong, unstabilized dose. It burns off chloramines, body oils, and other organic load after heavy use, storms, or an opening, and adds no CYA. It comes as dry granules in 1-lb bags, so it's easy to store and carry compared with jugs.

How to use:

1. Brush the pool, empty the baskets, and confirm the filter is clean. Pump on.
2. Fill a clean 5-gal bucket about ¾ with pool water, then add the granules to the water. Never add water to the granules. Stir with a clean stick and let the undissolved residue settle.
3. Pour the solution slowly around the deep end or in front of a return, at dusk. Over plaster, some labels allow broadcasting dry. Over vinyl or fiberglass, always pre-dissolve: undissolved granules sitting on a liner bleach and weaken it.
4. Run the pump at least 8 h, brush again, then test FC and CC.
5. Swim only when FC has fallen to your label's re-entry limit.

How much (per 10,000 gal) · basis: label + stoichiometry

To hit a specific FC, use the dose card above.

Cautions:

• Each shock leaves calcium behind: about +7 ppm CH per 10 ppm FC. That's harmless in a soft-water plaster pool and a scaling problem in a high-CH pool or on an SWG cell.
• Fixed "1 lb per 10,000 gal" directions ignore CYA. A 5–10 ppm shock is weak above CYA ~50 (§1.4).
• For multi-day SLAM, use liquid chlorine (A1 · O1). Five days of SLAM with cal-hypo can add 40–70 ppm CH.
• Undissolved residue and temporary cloudiness are normal. Brush them out.

Effect & benefit: Day-to-day chlorine without adding CYA, either from cal-hypo tablets in a dedicated cal-hypo feeder (common on commercial pools) or from small granular doses. It suits indoor pools (no CYA wanted) and pools that also need calcium.

How to use:

1. Tablets: use only a feeder built for cal-hypo tablets: Accu-Tab Blue (68%) or Pulsar Plus briquettes (≥ 65% available, ~7 g each). Never use a trichlor feeder, and never mix product types in one feeder.
2. Set the feeder to hold FC at target. Accu-Tab Blue's label says to adjust to 1–3 ppm. For outdoor pools with CYA, scale the target to CYA (§1.4).
3. Test FC daily the first week and adjust the feeder setting.
4. Granular: pre-dissolve small daily doses in a bucket of pool water, as in L1.
5. Test CH monthly. It climbs steadily (see O1).

How much (per 10,000 gal) · basis: label + stoichiometry

Cautions:

• The "industrial" Accu-Tab (325 g tablets, EPA 748-295) is labeled not for swimming pools. Buy the pool-registered Accu-Tab Blue.
• CH rises about 0.7 ppm for every ppm of FC you add.
• Calcium scale can clog feeder outlets; descale per the feeder maker.

Effect & benefit: A doubled shock kills suspended and early wall algae. HTH tells users to double the dose for cloudy water or early algae. Brushing is what exposes the algae to the chlorine.

How to use:

1. Brush every surface hard. Use a stainless brush on black-algae spots, on plaster only.
2. Pre-dissolve and add the doubled dose (as in L1), pump running 24 h.
3. Brush daily, vacuum dead algae (to waste if heavy), and clean the filter.
4. If the water isn't clear and holding chlorine overnight within 2–3 days, switch to a full SLAM with liquid chlorine (A1 · O1).

How much (per 10,000 gal) · basis: label + stoichiometry

Cautions:

• One big dose often only knocks algae back. Holding a CYA-indexed level is what finishes it (A1 · O1).
• Very high FC bleaches the pH reagent (§1.7).

Effect & benefit: Every ppm of FC from cal-hypo leaves ~0.7 ppm CH behind. If your fill water is soft and a plaster pool sits below its calcium target, using cal-hypo as the daily chlorine for a few weeks raises CH "for free." You don't buy or dissolve calcium chloride, and the water stops being aggressive to the plaster.

How to use:

1. Test CH, TA, pH, and CYA and work out CSI (§1.6). This only makes sense if CH is below target and CSI is negative.
2. Switch your daily chlorine from liquid chlorine to pre-dissolved cal-hypo (L1/L2 method).
3. Retest CH weekly.
4. When CH reaches target, or CSI approaches 0, switch back to liquid chlorine.
5. If you need a big CH jump fast, use calcium chloride (F1) instead. Cal-hypo only adds calcium as fast as you use chlorine.

How much (per 10,000 gal) · basis: stoichiometry (0.706 ppm CH per ppm FC)

For per-pound FC and CH by strength, see the dose card above (e.g., 1 lb of 73% ≈ +8.8 ppm FC and +6.2 ppm CH). The 0.7 ratio counts only the hypochlorite. Blends with extra calcium salts add a little more, so treat 0.7 as a floor.

Cautions:

• Not for SWG pools (scale on the cell) or pools already at or above target CH.
• Watch for cloudiness, a sign CSI has gone positive. Return to liquid chlorine if you see it.

Effect & benefit: Granules sealed in a sock deliver very concentrated chlorine directly onto one spot without dosing the whole pool to that level. Black-algae colonies hide under protective layers; after you break them with a stainless brush, the sock's local blast penetrates. Leaf and berry stains on plaster lighten in minutes.

How to use:

1. Wear gloves and goggles.
2. Put 2–4 oz of cal-hypo in a clean cotton sock or nylon knee-high and knot it closed. Use a new sock that has never touched trichlor or any other chemical.
3. For black algae, scrub the spot hard with a stainless-steel brush first.
4. Turn the pump off. Hold the sock against the spot, or drag it slowly over it, for 30–60 s at a time. A sock tied to a pole or brush head reaches deep spots. Don't leave it lying there.
5. Repeat on each spot, brush again, then restart the pump.
6. Dissolve any granules left in the sock in a bucket of pool water and pour that into the pool. Never return a wet sock to the chemical container.
7. For black algae, repeat daily alongside a SLAM (A1 · O1).

How much (per 10,000 gal) · basis: rule of thumb (per sock) + stoichiometry (FC added)

Cautions:

• ⛔ Never on vinyl, fiberglass, or painted surfaces: it bleaches and damages them.
• Colored plaster and pebble finishes can lighten; test an inconspicuous spot.
• A sock left resting in one spot can bleach a pale halo into plaster.

Effect & benefit: When there's no plain household bleach, EPA's emergency-disinfection page describes making a chlorine stock solution from granular calcium hypochlorite, then diluting it into clear water to kill bacteria and viruses. It doesn't remove chemical contamination.

How to use (EPA's words, quoted):

"Add one heaping teaspoon (approximately ¼ ounce) of high-test granular calcium hypochlorite (HTH) to two gallons of water and stir until the particles have dissolved. The mixture will produce a chlorine solution of approximately 500 milligrams per liter. To disinfect water, add one part of the chlorine solution to each 100 parts of water you are treating. This is about the same as adding 1 pint (16 ounces) of the chlorine solution to 12.5 gallons of water."

1. Use a product whose only active ingredient is calcium hypochlorite, ideally 65–73%. Avoid blends with clarifiers, algaecides, or "blue" additives, and never use dichlor or trichlor.
2. Filter cloudy water through a clean cloth first.
3. After adding the stock, stir and let the water stand at least 30 minutes before drinking. That's the same contact time EPA gives for its bleach method.
4. Label the stock container "POISON — chlorine stock, do not drink." Make it fresh; it weakens over days.

How much · basis: label (EPA) + stoichiometry

For reference, ¼ oz of 56–73% product in 2 gal works out to ~520–680 mg/L. "Approximately 500" covers a loosely heaped teaspoon, and the 1:100 dilution lands at ~5 mg/L.

Cautions:

• FIFRA: pool-shock labels don't list drinking water. This is EPA's emergency procedure for when nothing better exists.
• Store the dry product sealed and dry. The stock solution is corrosive.

Effect & benefit: An unstabilized shock that dissolves completely in seconds and adds no calcium and no CYA. Granules don't sit on a liner and bleach it, and nothing clouds the water. That made it the classic shock for vinyl, fiberglass, spas, and SWG pools. It's also a quick chlorine boost when you don't want any CH or CYA side effects.

How to use:

1. Pump on, filter clean.
2. Broadcast the granules over the deep end, or pre-dissolve them in a bucket of pool water. Always add granules to water.
3. Brush, run the pump at least 8 h, then test FC.
4. Swim per the label's re-entry limit.

How much (per 10,000 gal) · basis: stoichiometry

Use the dose card. A typical 5–10 ppm shock is 19–38 oz (1.2–2.4 lb). Retest after dosing: old stock may have weakened, so the dose card is a ceiling, not a guarantee.

Cautions:

• Per ppm of chlorine, it costs several times what liquid chlorine costs.
• Caked or damp product may have lost strength or contaminated itself. Dispose of it through a household-hazardous-waste drop-off.

Effect & benefit: Granular chlorine that dissolves in seconds and barely moves pH. Small, precise doses are easy, which is why it's the classic hot-tub sanitizer. The built-in stabilizer keeps chlorine from burning off in sun. The catch: CYA rises with every dose.

How to use:

1. Test FC (and CYA every couple of weeks; it climbs fast).
2. Spa: after each soak, sprinkle the dose into the water with the jets running. Pool: broadcast over the deep end with the pump running, or pre-dissolve in a bucket of pool water.
3. Retest FC before the next use.
4. When CYA reaches your target, switch to unstabilized chlorine (A1). That's the "dichlor-then-bleach" pattern (O1).

How much (per 10,000 gal) · basis: label + stoichiometry

Spa (400 gal) · basis: stoichiometry

Use a small kitchen scale. Weigh once, then mark a measuring spoon for your dose.

Cautions:

• At 10 ppm FC a week, a pool gains ~9 ppm CYA a week, roughly 36 ppm a month. The minimum FC rises with it (§1.4).
• In spas, plan a drain-and-refill on schedule. That resets CYA and TDS.

Effect & benefit: Dichlor dissolves almost completely and is near-neutral, so it can be broadcast over vinyl, fiberglass, and spa shells at shock doses with little risk of bleaching or residue. That's why "swim in 15 minutes"-style blends (e.g., XtraBlue) are built on it.

How to use:

1. Pump on. Broadcast over the deep end in front of a return, or pre-dissolve for very lightweight liners.
2. Brush, run the pump at least 8 h, and test FC and CC.
3. Swim per your label.

How much (per 10,000 gal) · basis: label + stoichiometry

The FC and CYA columns are our arithmetic. One label's printed ppm doesn't match its own dose, so trust the math.

Cautions:

• Every 10 ppm of dichlor shock adds ~9 ppm CYA. Repeated dichlor shocking is the fastest way to over-stabilize a pool. For SLAM, use liquid chlorine (A1 · O1).
• Copper-containing blends (XtraBlue: 0.26% Cu) add ~0.03 ppm copper per lb per 10,000 gal, and copper only leaves by dilution. A pound a week for 20 weeks can approach 0.6 ppm, well past the ~0.2 ppm where blue-green stains and green hair start. That's especially bad with SWG cells and later ascorbic-acid treatments.

Effect & benefit: When CYA is below target (fresh water, after rain dilution, after a drain), dichlor raises FC and CYA together. You don't need to sock-dissolve stabilizer separately.

How to use:

1. Test CYA and decide the target (outdoor chlorine 30–50; SWG per cell maker).
2. Use dichlor for your chlorine doses until CYA reaches target.
3. Switch to unstabilized chlorine, or the SWG, before you overshoot.
4. Retest CYA weekly while doing this.

How much (per 10,000 gal) · basis: stoichiometry (0.91 ppm CYA per ppm FC)

Cautions:

• CYA leaves only by dilution or a biological reducer (D2).
• Overshooting costs a partial drain.

Effect & benefit: A fresh fill has CYA 0, so outdoor chlorine burns off within hours. Dosing dichlor for the first days builds the stabilizer with the same product that sanitizes. In spas, this is the well-known "dichlor-then-bleach" routine: dichlor until CYA ≈ 30, then plain bleach, so CYA stops climbing.

How to use:

1. Test CYA (expect 0 after a fill) and pick a target: ~30 for a spa, 30–50 for an outdoor pool, or the cell maker's range for SWG.
2. Pool: add dichlor in portions, about +10 ppm CYA per day. Each portion also brings ~11 ppm FC. Keep swimmers out until FC falls to your label's re-entry limit. Retest CYA after the last portion; dichlor's CYA reads right away.
3. Spa: use dichlor for the normal after-soak doses (about +3 ppm FC, which adds +2.7 ppm CYA each). After roughly 11 doses CYA is near 30, so switch to liquid chlorine.
4. From then on, chlorinate with liquid chlorine (A1). Top up CYA only after dilution.

How much (per 10,000 gal) · basis: stoichiometry

For a 400 gal spa, +30 ppm CYA takes ~3.1 oz (89 g) of 56% in total. Normally you spread it across the routine doses rather than adding it at once.

Cautions:

• For big pools, granular stabilizer (D1) plus liquid chlorine is cheaper. Dichlor bootstrapping makes sense when you need the chlorine anyway.
• On day one the FC-to-CYA ratio is very high (FC 11 with CYA 10), so honor the label's re-entry limit.

Effect & benefit: Granules sprinkled right onto an algae spot dissolve on it and give a local burst of chlorine. Dichlor is near-neutral, so it's gentler on plaster than resting trichlor.

How to use:

1. Brush the spot hard. Use a stainless brush on plaster for black algae.
2. Turn the pump off.
3. Sprinkle 1–2 oz of granules from just above the water so they land on the spot. A pole-mounted cup reaches deep spots.
4. Wait 15–30 min, brush again, and restart the pump.
5. Repeat daily alongside whole-pool treatment (A1 · O1).

How much (per spot; counts toward the pool) · basis: rule of thumb + stoichiometry

Cautions:

• ⛔ Not on vinyl or fiberglass, where resting granules bleach spots.
• Colored plaster and pebble finishes can lighten; test first.

Effect & benefit: Slow-dissolving tablets meter chlorine into the water around the clock, and their built-in CYA protects that chlorine from sunlight. It's the most hands-off chlorine source, which is why it's on every store shelf.

How to use:

1. Put tablets in a floater (adjust the vents) or an in-line or off-line erosion feeder. The feeder must be installed after the heater, with a check valve, per the feeder and heater instructions.
2. Start at the label rate below. Test FC daily for the first week, then adjust the vents or dial.
3. Top up with liquid chlorine (A1) on hot or busy days. Tablets rarely keep up with peak summer demand alone.
4. Test CYA monthly (L2) and TA weekly. Tablets drag TA and pH down, so offset with baking soda (E6).
5. Never let tablets rest on a step or the floor, and don't use the skimmer basket if a heater or salt cell is downstream.

How much (per 10,000 gal) · basis: label + stoichiometry

Summer losses of 1–4 ppm/day mean many pools need 2–4 tablets a week, or tablets plus liquid chlorine.

Metals in multi-function tablets (per 8-oz tablet per 10,000 gal; they accumulate):

Boric-acid tablets add negligible borates.

Cautions:

• Copper tablets cause blue-green stains and green hair, and copper plates SWG cells.
• Acidic, concentrated water inside feeders and skimmers corrodes heater heat exchangers and metal parts.
• See L2 for CYA creep.

Effect & benefit: Each tablet adds CYA, which keeps chlorine from burning off in sun. That's helpful until CYA reaches target. After that CYA keeps climbing ("CYA creep"), and since the minimum FC is about 7.5% of CYA, you need ever more chlorine just to stay safe. More chlorine means more tablets, which means more CYA: a vicious circle that ends in a cloudy or green pool.

How to use:

1. Test CYA monthly while on tablets.
2. When CYA reaches the top of your target (≈ 50 for most manually chlorinated pools), switch to liquid chlorine (A1) and let splash-out, backwash, and rain dilute CYA.
3. Restore TA lost to tablet acidity with baking soda (E6).
4. If CYA is already high, partial drain and refill. Dilution is the only cheap fix (D2 is the alternative).

How much (per 10,000 gal, 8-oz tablets, no dilution) · basis: stoichiometry

The minimum FC needed climbs with CYA:

Cautions: Real pools lose some CYA to dilution, so measure rather than trusting the table. CYA leaves only by dilution or D2. Plan the season's switch to unstabilized chlorine before you hit the wall.

Effect & benefit: A free, 60-second test that tells organic stains from metal stains, so you pick the right treatment. Concentrated chlorine bleaches organic stains (leaves, berries, algae, tannins) almost immediately but does nothing to metal stains.

How to use:

1. Put on chemical gloves and goggles. Hold a 3" tablet, or clamp it in a pole-mounted holder for deep spots.
2. Press and rub the tablet on the stain for 30–60 s.
3. Lightens → organic. Treat with chlorine: A1 · O7, A2 · O2, or a SLAM.
4. No change → try the vitamin C test (I3 · O2). If vitamin C lightens it, it's metal.
5. Put the now-wet tablet in your floater or feeder. Never return it to the dry tablet bucket.

How much (per 10,000 gal) · basis: rule of thumb

One tablet per test. Only a few grams dissolve, which adds a negligible amount of FC and CYA to the pool.

Cautions:

• Rinse the spot with pool water afterward.
• On vinyl, test only a tiny inconspicuous area, or skip the test: trichlor bleaches liner prints.
• Never leave the tablet resting on the surface.

Effect & benefit: SWG pools (and pools with waterfalls, spillovers, or bubblers) drift up in pH, so you add acid every few days. Trichlor is acid plus chlorine plus CYA in one tablet. A tablet or two in a floater shifts part of the chlorine load off the cell, cuts the muriatic acid you'd otherwise pour, and replaces CYA lost to splash-out and rain. That's three jobs with one product, as long as you stop before CYA overshoots.

How to use:

1. Test CYA, FC, and pH, and confirm CYA is below your cell maker's target (often 60–80).
2. Put 1–2 tablets in a floater. Tether it away from steps so it can't park on a surface. Never use the skimmer or an in-line feeder upstream of the cell.
3. Turn SWG output down a little so FC doesn't overshoot. Each 8-oz tablet supplies about a week's worth of 0.8 ppm/day per 10,000 gal.
4. Track how much less acid you need. Test CYA every 2 weeks and pull the floater when CYA reaches target.

How much (per 10,000 gal) · basis: stoichiometry

Cautions:

• The acid credit only works while you want CYA. After that it becomes CYA creep (L2).
• Avoid copper-containing multi-function tablets in SWG pools: copper plates on the cell.

Effect & benefit: The cell needs enough dissolved chloride (conductivity) to make chlorine.

• Too low: output drops, "low salt" warnings appear, and plate wear rises.
• Too high: many cells shut down, and corrosion risk to metal fixtures and stone rises.

Holding the maker's range keeps chlorine production steady with no jugs or tablets.

How to use:

1. Test salt independently with a titration strip or calibrated meter. Cell readouts drift.
2. Calculate from the table below, then plan to add about 75–80% first. Over-salting is only fixed by draining.
3. Turn the cell off (or set output to 0) and leave the pump running.
4. Broadcast the salt over the deep end, not into the skimmer, and brush the floor until it dissolves. Don't let piles sit.
5. Keep the cell off until the salt has fully dissolved and circulated. Your cell manual gives the wait time.
6. Retest, add the remainder if needed, then restart the cell.

How much — to reach a target from your current salt (99.8% NaCl, per 10,000 gal) · basis: stoichiometry

Converting from a traditional chlorine pool? Test first. Long-running bleach pools often already carry 1,000–2,000 ppm.

Cautions:

• Over-salted? The only fix is dilution: fraction to replace = (current − target) ÷ (current − fill). Example: 4,500 → 3,400 with 200 ppm fill water means replacing ~26%.
• Salt water is harder on natural stone coping, some deck materials, and exposed metal. Rinse splash zones.
• Recheck salt after heavy rain, backwashing, or a partial drain.

Effect & benefit: Pure pool salt is the same chemical as softener "solar salt." Leftover bags can refill a softener's brine tank instead of sitting in the shed.

How to use:

1. Confirm the pool salt is ≥ 99–99.8% NaCl with no additives, and check that your softener manual allows crystal or solar salt. Some recommend pellets.
2. Pour it into the brine tank. Coarse solar crystals are the closest match. Finer evaporated pool salt works in most tanks but can compact into "mush" in some.
3. Don't mix in rust-remover softener salts if your manual warns against mixing types.

How much (per brine tank, not per pool) · basis: label (softener manual) + rule of thumb

Fill to the level your softener's manual specifies. Many say to keep the salt above the water line and the tank at least one-quarter full. The softener's controller meters what each regeneration uses.

Cautions: Pool salt containing any additive doesn't belong in a softener, and softener salts with rust-remover additives don't belong in a pool.

Effect & benefit: Salt lowers the freezing point of ice water. The brine gets well below 32 °F, so it freezes a hand-crank ice cream fast or chills drinks in a cooler in minutes instead of an hour.

How to use:

1. Ice cream: layer ice and salt around the canister in the outer bucket, add a little cold water to start the brine, then churn. Keep the canister lid sealed so no brine gets in.
2. Drinks: stir salt into a cooler of ice and water. Submerged cans and bottles chill much faster than in ice alone.
3. Afterward, dump the brine on gravel or down a drain, not on grass or plants.

How much (per batch, not per pool) · basis: rule of thumb

Cautions:

• Pool salt isn't labeled as food grade. Keep it in the outer bucket and wipe the canister before opening.
• Brine kills lawns and corrodes metal coolers' hinges. Rinse afterward.

Effect & benefit: Gas chlorination was historically the cheapest chlorine per pound, adds no calcium, CYA, or extra salt, and is easy to automate. Its drawback is a toxic, pressurized gas that needs a dedicated, ventilated room, leak detection, training, and permits.

How to use: Licensed, trained operators only, under the local health code and the equipment maker's procedures. A vacuum-operated gas chlorinator meters gas into the return line, with automatic shutoff and leak detection. Base must be fed alongside to counter the acid. There is no safe do-it-yourself version, so this guide gives no procedure.

How much (per 10,000 gal) · basis: stoichiometry

Cautions: Never attempt this outside a licensed commercial installation. Many jurisdictions restrict or prohibit gas chlorine at public pools.

Effect & benefit: A steady bromine residual sanitizes and oxidizes. Bromine has three advantages over chlorine:

• It stays ~90% active at pH 7.8 (§1.5).
• Its combined forms (bromamines) still sanitize and smell less than chloramines.
• A feeder delivers it for a week at a time.

How to use:

1. Confirm the site is allowed: an indoor pool, or a spa that stays covered when not in use.
2. Load an erosion feeder plumbed after the heater, with a check valve, or use a floater. Never put tablets in the skimmer: concentrated bromine water corrodes the pump and heater.
3. Start at a middle feeder setting.
4. Test bromine daily for the first week (DPD; bromine = chlorine-scale reading × 2.25) and turn the dial to hold the label target.
5. Refill before the feeder runs empty.
6. To start up or catch up quickly, don't overload the feeder. Build a bromide bank (B3) and oxidize it with liquid chlorine (A1 · O3) or MPS (C1 · L2).
7. Shock weekly or after heavy use to burn off organics and reactivate spent bromide.

How much (per 10,000 gal) · basis: label

At the residential rate, a 10,000-gal pool receives ≈ 11.6 ppm of bromine capacity per week (≈ 1.7 ppm/day), which matches typical indoor demand.

Target residuals:

Cautions:

• Tablets are acidic: watch pH and TA, and top up with baking soda (E6).
• DMH accumulates: about 4–5 ppm a week at the residential rate, and only dilution removes it. High DMH slows bromine, so plan regular partial drains, especially in spas.
• CYA does not protect bromine.
• ⛔ Never load chlorine tablets into a bromine feeder, or the reverse.

Effect & benefit: Every bromine atom a tablet delivers ends up as bromide after it does its work. Over weeks, a tablet-fed pool accumulates a bromide reserve. Any oxidizer — a chlorine shock, MPS, or ozone — can then turn it back into active bromine instantly. That is why weekly shocking works so well in bromine pools.

How to use:

1. Run tablets as in L1. The bank builds on its own.
2. For a full bank from day one, add sodium bromide (B3 · L1).
3. Shock weekly with liquid chlorine (A1 · O3) or MPS (C1 · L2) to regenerate bromine and oxidize organics.
4. After a partial drain, the bank drops in proportion to the water replaced.

How much (per 10,000 gal) · basis: stoichiometry

Cautions:

• Bromide is permanent. Switching back to chlorine or SWG requires draining (§2.5).
• With a bank present, every chlorine dose becomes bromine, which sunlight destroys.

Effect & benefit: Bromine tablets in a small floater keep recirculating fountains, waterfalls, and water walls free of bacterial slime and algae. Bromine tolerates the high pH that constant aeration creates.

How to use:

1. Use only in water nobody drinks: no fish, no birdbaths, no pet access, no wildlife watering. Prefer indoor, shaded, or covered features. Sunlight makes bromate here exactly as in a pool.
2. Clean the basin and pump.
3. Put tablets in a small floater, or in an in-line feeder for larger features.
4. After 24 h, test with bromine strips. Add or remove tablets to hold 1–3 ppm.
5. Replace evaporated water with fresh water. Drain and refill periodically, since DMH and minerals concentrate as water evaporates.

How much · basis: stoichiometry + rule of thumb

Cautions:

• FIFRA: a pool-labeled product used in a fountain is off-label. Choose a BCDMH product whose label lists decorative fountains or water features.
• Bromine corrodes copper, bronze, and some fountain pumps.
• ⛔ Fish ponds, birdbaths, pet bowls, potable water.

Effect & benefit: The same job as BCDMH, with all of its oxidizing power delivered as bromine. Per pound it leaves a little less DMH and a little more bromide.

How to use:

1. Follow the product label for feeder or granular dosing.
2. Hold the label's bromine target (spas typically 2–4 ppm residential).
3. Shock weekly to regenerate the bank.

How much (per 10,000 gal) · basis: label + stoichiometry

Follow your label. As a check, 1.20 oz of 99.4% DBDMH supplies about +1 ppm of bromine capacity per 10,000 gal. For a 400-gal spa that's ≈ 1.4 g per ppm.

Cautions:

• Supply is thin. Most "bromine tablets" are BCDMH or BCDMH-rich blends.
• The same DMH, CYA, and outdoor-use limits as B1 apply.

Effect & benefit: A bromide bank lets any oxidizer produce bromine on demand. This makes start-up immediate and lets a spa run on "two-part bromine": sodium bromide plus MPS, chlorine, or ozone, with no tablets and no DMH. A 30 ppm bank could, fully oxidized, supply ~60 ppm of bromine (as Br₂). The oxidizer, not the bromide, is what limits your residual.

How to use:

1. Confirm the site is allowed: an indoor pool or a covered spa.
2. Balance pH 7.2–7.8 and TA 80–120 first.
3. With the pump running, dissolve granular in a bucket of pool water (or broadcast it), or pour liquid in front of a return.
4. Oxidize to make bromine: liquid chlorine (A1 · O3) or MPS (C1 · L2).
5. Test with DPD (bromine = chlorine-scale reading × 2.25).
6. After any partial drain, re-add in proportion. For example, replacing 25% of the water calls for 25% of the original dose.

How much · basis: label (spa) + stoichiometry (pool)

Cautions:

• Bromide is permanent until you drain.
• With ozone, bromide also forms bromate, so spa ozonators and bromide banks need the maker's blessing.
• In an SWG pool, the cell converts bromide to bromine, which CYA can't protect.

Effect & benefit: A few ppm of bromide, followed by a heavy chlorine shock, puts some bromine in the water, and bromine is claimed to reach yellow/mustard algae better than chlorine alone. Most "yellow" products are exactly this. (Natural Chemistry's Yellow Out is different: it's ammonium sulfate — see G5.)

How to use:

1. Read the label first. Current US sodium-bromide boosters are labeled not for use in outdoor pools. Most mustard-algae pools are outdoors, so using them there is a FIFRA violation. A SLAM at the mustard level (A1 · O1) treats the same algae with no bromide.
2. Brush walls, floor, steps, and behind ladders.
3. With the pump running, add the booster per label.
4. Shock with chlorine at the label rate, often double the normal shock.
5. Run the pump 24 h, brush daily, vacuum, and clean the filter.
6. Disinfect swimsuits, toys, brushes, and the vacuum head (A1 · O5).

How much (per 10,000 gal) · basis: label (dose) + stoichiometry (bromide added)

Cautions:

• It's permanent. Every future chlorine dose partly becomes bromine, which sunlight destroys because CYA can't protect it. Expect chlorine use to climb until you drain.
• In SWG pools, the cell will generate bromine from then on.
• Outdoors, bromine plus sunlight forms bromate, which is why the label changed.

Effect & benefit: Run a bromine pool or spa without BCDMH. You get no DMH buildup, lower cost, and exact control: each chlorine dose becomes the same oxidizing amount of bromine within minutes. It's pH-neutral overall, so pH drifts less than with acidic tablets.

How to use:

1. Start with fresh, balanced water: pH 7.2–7.8, TA 80–120, no biguanide.
2. Add sodium bromide for a 15–30 ppm bank (L1 table).
3. Add liquid chlorine to your bromine target. It converts within minutes; full table in A1 · O3.
4. Test daily with DPD (× 2.25) and dose chlorine as needed. After each partial drain, top the bank back up in proportion.

How much · basis: stoichiometry

Cautions:

• Indoor pools and covered spas only (US labels).
• Any CYA in the water does nothing for bromine.
• Don't run an SWG cell in this water unless you mean to make bromine.
• Spa ozonators plus bromide form bromate.

Effect & benefit: MPS burns off sweat, oils, urine compounds, and the precursors that become chloramines, without raising chlorine. Swimmers can get back in within minutes rather than waiting for a chlorine shock to fall. It also lowers sanitizer demand after heavy use.

How to use:

1. Test pH. MPS works across the normal range; it will nudge pH down.
2. Broadcast it with the pump running, or pre-dissolve it in a bucket of pool water and pour in front of a return. Evening or right after heavy use is best.
3. Keep circulating. Re-enter per your label (see below).
4. When you next test combined chlorine, use an MPS-deactivating reagent. Otherwise leftover MPS reads as CC (§1.7).
5. Keep FC or bromine in range separately. MPS doesn't replace the sanitizer.

How much (per 10,000 gal) · basis: label

Cautions:

• Not a sanitizer and not an algae treatment: 1 lb ≈ 2.4 ppm of FC-equivalent oxidation.
• Regular use lowers pH and TA and adds sulfate. Over years that matters for plaster and grout (§1.2).
• MPS reads as CC on DPD tests until it's consumed.

Effect & benefit: With a bromide bank in place, MPS oxidizes bromide to active bromine. This is the classic "non-chlorine bromine" spa system: sodium bromide plus MPS, with no tablets, no chlorine smell, and no DMH. It also oxidizes the organics each soak leaves behind.

How to use:

1. Establish the bank: B3 · L1, e.g. ½ oz sodium bromide per 100 gal → ~30 ppm.
2. After each use, or as the label directs, add MPS with the jets running.
3. Test bromine (DPD × 2.25). If a reading right after dosing looks implausibly high, retest with the MPS-deactivating step.
4. Expect pH and TA to drift down over weeks. Restore TA with baking soda (E6).

How much · basis: label + stoichiometry

Follow your label. As a cross-check, each 1 mol of KHSO₅ makes 1 mol of bromine:

Cautions:

• Indoor pools and covered spas only (bromide label restriction).
• Weigh small spa doses. A heaping scoop can be 2–3× the intended amount.

Effect & benefit: MPS is acidic, and the oxidation reaction releases more acid as it's spent. In a spa whose pH creeps up from jet aeration, routine MPS dosing can hold pH steady with little or no separate acid. It isn't worth buying as an acid, though.

How to use:

1. Dose MPS as you normally would (L1 or L2).
2. Track pH and TA weekly.
3. If pH holds in range, skip the separate acid dose. If TA falls below ~60–80, add baking soda.

How much · basis: stoichiometry

About a third of the drop happens immediately and the rest as the MPS is consumed. For comparison, the same 10 ppm TA drop takes 25.6 fl oz of 31.45% muriatic acid (E1).

Cautions:

• Pound for pound it's many times the price of muriatic acid or dry acid.
• It adds potassium and sulfate to the water.

Effect & benefit: Destroys free chlorine and bromine in minutes. It's the fastest way to:

• get under your label's swim limit after an over-shock,
• drain or backwash without killing a lawn,
• reach FC 0 before an ascorbic-acid stain treatment (I3 · O1).

The only byproducts are oxygen and chloride (or bromide). It leaves no sulfur compounds behind, as thiosulfate and sulfites do.

How to use:

1. Test FC (or bromine) and decide the target. Usually that's the top of your normal range, not zero.
2. Calculate from the dose card and add about 75% of it.
3. Pour slowly in front of a return with the pump running. Fizzing is oxygen being released.
4. Circulate 30 min, retest, and finish the dose.
5. If you overshoot, leftover peroxide will eat the next chlorine you add. Either wait (sunlight and time break it down) or keep adding chlorine until FC holds.

How much (per 10,000 gal) · basis: stoichiometry, cross-checked with field reports

• Use the dose card above.
• Field checks:
  • Trouble Free Pool reports that 1 gal of a ~27% product lowers FC by ~55 ppm in 10,000 gal. Stoichiometry predicts ~62.
  • In The Swim reports that 7 fl oz of 27% lowers FC by ~3 ppm. Stoichiometry predicts ~3.4.
• Both agree within normal measurement and strength losses.

Cautions:

• 27–35% peroxide causes chemical burns (skin turns white) and eye damage: goggles and gloves.
• ⛔ Never pour it into a chlorine jug or a bucket of chlorine, and never the reverse.
• Store it vented, cool, and dark. It slowly decomposes and the bottle builds pressure.

Effect & benefit: Biguanide (PHMB) reacts with chlorine and forms a gummy, staining precipitate. Every conversion starts at FC 0. Peroxide gets you there in an afternoon instead of the days chlorine takes to fade.

How to use:

1. Turn off the SWG (and remove or bypass the cell) and stop all chlorine products.
2. Bring FC to 0.0 with peroxide (dose card), confirmed with a DPD test.
3. Clean or replace the filter media.
4. Follow the biguanide maker's conversion procedure exactly. Some require metals-free water or fresh media.
5. Never add chlorine or bromine afterward.

How much (per 10,000 gal) · basis: stoichiometry

Cautions:

• Biguanide is incompatible with chlorine, bromine, copper algaecides, and many clarifiers and sequestrants. The conversion is hard to reverse, and going back is the harder direction.

Effect & benefit: UV in sunlight destroys unbound chlorine fast. An unstabilized outdoor pool can lose most of its FC in a few hours of strong sun. CYA holds chlorine in a bound reserve that UV mostly can't break, and releases it as the active part is used. Chlorine then lasts days instead of hours, and a salt cell can run far fewer hours.

The trade-off: less of the FC is active HOCl at any moment, so the FC you keep must scale with CYA (§1.4).

How to use:

1. Test CYA and pick a target.
   • Outdoor manual chlorine: 30–50 (PHTA ideal; TFP 30–60).
   • SWG: 60–90 (TFP; most cell makers 60–80).
   • Indoor pools: 0–20.
   • Bromine: 0.
   • Many public codes cap CYA around 100.
2. Calculate the dose from the table below. Near the top of your range, add ~75–80% first, because CYA comes out only by dilution.
3. Granular dissolves slowly (2–7 days). Choose one method:
   • Put it in a clean sock or fine mesh bag. Hang the bag in front of a return jet, or set it in the skimmer basket with the pump running, and knead it now and then.
   • Pour it slowly into the skimmer with the pump running. A sand or DE filter catches undissolved crystals, which dissolve there.
   • Don't broadcast it onto the floor. Undissolved acidic granules can sit on plaster or vinyl for days.
4. Liquid: shake well and pour slowly in front of a return with the pump running. It disperses immediately.
5. Don't backwash or clean the filter for about a week. Undissolved CYA in the filter would go to waste.
6. Retest CYA after ~7 days for granular, or 1–2 days for liquid. Then reset your FC target to the new CYA (§1.4).
7. Retest pH after granular CYA has dissolved, and don't rush to correct it. Most of the dip recovers as the extra CO₂ outgasses (see Cautions).

How much (per 10,000 gal) · basis: stoichiometry (granular) + label (liquid)

Cautions:

• CYA leaves only by dilution (drain and refill, rain overflow, splash-out) or a biological reducer (D2). Overshooting is the expensive mistake. Remember that trichlor and dichlor keep adding it.
• High CYA needs high FC. At CYA 80 the minimum is 6 ppm and SLAM is 31 ppm (§1.4).
• Granular is a weak acid. In a closed-system model, +30 ppm at TA 80 can pull pH from 7.5 to about 7.1 while it dissolves, with the TA reading unchanged. Most of that recovers as the extra CO₂ escapes. Expect a smaller dip in a real, aerated pool.
• Liquid stabilizer is a base. Each gallon adds ≈ 12 ppm TA per 10,000 gal and nudges pH up. Count it in SWG pools, where you're already fighting pH rise.
• The CYA test is a turbidity test.
  • It's most accurate at ~30–90 ppm.
  • Below ~20 ppm it's unreliable.
  • Above ~100, dilute 1:1 with tap water and double the result.
  • Read it in consistent light, and warm cold samples first (§1.7).
• ⛔ Bromine pools: CYA does nothing to protect bromine from sunlight.

Effect & benefit: Indoors there's no sunlight to protect against, so CYA is usually left out. It does a second job, though. Because it holds most free chlorine in a bound reserve, the active HOCl at any moment is far lower for the same FC.

Trouble Free Pool's approach uses that on purpose: a small amount (~20 ppm indoors, ~20–30 ppm in spas), with FC scaled to match. Chlorine still sanitizes, but it's gentler on skin, hair, swimsuits, liners, and spa covers. TFP's reasoning is that lower HOCl also slows the reactions that create chloramine and byproduct odors. In hot tubs, the "dichlor-then-bleach" routine (A4 · O1) lands at ~30 ppm CYA for exactly this reason.

How to use:

1. Check your code first. Public and commercial pools and spas follow their health code, which may prohibit or cap stabilizer indoors or in spas. This is a residential technique.
2. Pick a target: ~20 ppm for an indoor pool, ~20–30 ppm for a spa.
3. Spa: put granular in a sock in the filter compartment or skimmer with the jets running (hot water dissolves it faster), or use liquid stabilizer, or build it with dichlor doses (A4 · O1). Pool: use the L1 method.
4. Re-index FC to the CYA.
   • CYA 20: minimum ≈ 1.5 ppm, typically 2–4.
   • CYA 30: minimum 2, target 4–6 (§1.4).
   • Spas are dosed after each soak.
5. After a spa drain and refill, CYA starts at 0 again; repeat.

How much · basis: stoichiometry (granular) + label (liquid)

Cautions:

• CYA without matching FC is a weak pool: CYA 30 with FC 1 sanitizes poorly. Keep FC at the §1.4 level.
• Stabilizer alone isn't an EPA-registered pesticide, so FIFRA doesn't restrict this use. Health codes may, and the chlorine product's label still governs how you chlorinate.
• Not for bromine spas: CYA doesn't help bromine.

Effect & benefit: Brings over-stabilized water (CYA ~80–100+) back down when draining is impractical:

• drought restrictions,
• a high water table (risk of floating the shell),
• costly or very hard fill water,
• a vinyl liner that can't be drained far.

Lower CYA restores normal FC targets and makes a SLAM affordable again.

How to use:

1. Confirm CYA accurately: dilute 1:1 if it reads over 100 (§1.7). Note the water temperature.
2. Set the conditions on the Bio-Active label:
   • FC 1–5 ppm (not 0; 5 ppm and above degrades the culture)
   • pH 7.2–7.8
   • TA 80–120
   • water above 65 °F (it stops working below 35 °F or above 140 °F)
3. Timing: no shock in the 72 h before, and no algaecide or clarifier in the week before.
4. Pour the entire pouch into the skimmer with the pump running, and run the pump at least 4 h.
5. For the next 7–10 days, hold FC at 1–5: SWG output down, small liquid-chlorine doses only, no shock.
6. Retest CYA at day 7–10. If it's still high, treat again after 7 days.
7. Afterward:
   • Re-index FC to the new CYA (§1.4).
   • Check CC and run an overnight loss test (A1 · O2). Nitrogen from the breakdown consumes chlorine, so expect to add more than usual for a few days.
   • SLAM if CC stays above 0.5.

How much · basis: label (dose) + stoichiometry (chlorine-demand ceiling)

Compare with dilution. With CYA-free fill water, fraction to replace = (current − target) ÷ (current − fill):

• Dilution is predictable, works at any temperature, and also lowers salt, TDS, and (with soft fill water) CH.
• The reducer saves water and avoids draining risks.

Cautions:

• Results vary, and retail claims conflict. Measure before and after rather than counting on a number.
• No effect when it's cold or chlorine is too high: below ~65 °F, or with FC ≥ 5 ppm, expect little or nothing.
• Watch for algae during the low-chlorine hold. FC 1–5 at high CYA is a weak sanitizer, so brush, keep the filter clean, and test daily.
• If you dilute instead:
  • Drain vinyl pools in steps; never lower the water past what the liner maker allows.
  • Don't drain plaster or fiberglass pools in high-water-table areas without professional advice (hydrostatic lift).

Effect & benefit: Brings pH back to 7.4–7.6. That keeps chlorine effective, keeps eyes comfortable, and stops calcium scale from forming on plaster, tile, heaters, and salt cells. In SWG pools and pools with water features, this is the routine chore.

How to use:

1. Test pH and TA. CYA and borates also matter: borates roughly double or triple the acid needed near pH 7.5–8.0 (§6.2).
2. Look up the dose below (or in §6.2 for your TA and CYA), then measure ~75% of it.
3. With the pump running, pour slowly and low into the deep end in front of a return, away from the skimmer and from any chlorine you've just added. Don't splash. Never pour acid into the skimmer of an SWG or heater pool.
4. Circulate 30–60 min, retest, and add the rest if needed.

How much (per 10,000 gal; TA 80, CYA 40, no borates) · basis: model

At other TA levels, the 31.45% amount for 7.8 → 7.4 is 9.8 fl oz at TA 60, 14.5 fl oz at TA 100, and 16.8 fl oz at TA 120. For CYA 0 and 70, see §6.2.

Cautions:

• Goggles and gloves. Fumes from an open jug corrode tools, and splashes burn.
• Store it away from chlorine. Keep the cap tight, and never store it above other products.
• Acid lowers TA every time you use it. Pools that need acid often benefit from lower TA, which means less drift.

Effect & benefit: High TA keeps pushing pH up as CO₂ escapes, so you add acid forever. The cycle below removes alkalinity on purpose. Acid lowers pH and TA together; aeration then raises pH back up without restoring TA. Repeat until TA is where you want it. Lower TA means less pH drift and less acid long-term.

How to use:

1. Decide the TA target. 60–80 suits most liquid-chlorine and SWG pools.
2. Add acid to bring pH to 7.0–7.2. Don't go below 7.0: plaster, grout, and copper heat exchangers suffer.
3. Aerate hard: point returns up to break the surface, run waterfalls or spa spillovers, add an air pump or bubbler. pH climbs as CO₂ leaves, typically over a day or two.
4. When pH reaches ~7.6–7.8, test TA, then repeat steps 2–3.
5. Stop at the target. Each cycle removes as much TA as the acid you added; aeration doesn't change TA at all.

How much (per 10,000 gal) · basis: stoichiometry (total) + model (per cycle)

Total acid is fixed by the TA you remove, however many cycles it takes. The dose card above gives the exact amount for each strength, e.g., 31.45%: 25.6 fl oz per 10 ppm. A typical cycle (pH 7.6 → 7.2 at TA 100, CYA 40) uses ~21 fl oz of 31.45% and removes ~8 ppm. Going from TA 120 to 80 therefore takes ~5 cycles and 3.20 qt (103 fl oz) of 31.45% in total.

Cautions:

• Keep FC at target throughout; low pH makes chlorine stronger and more irritating.
• Don't leave pH near 7.0 for days in a plaster pool.

Effect & benefit: White calcium scale on the cell's plates insulates them and cuts chlorine output. A short soak in diluted acid dissolves it. The acid is the same product you use for pH, so no special cleaner is needed.

How to use:

1. Check first: if the plates are clean, don't acid-wash. Every wash wears the plate coating.
2. Turn off power at the breaker. Close valves if needed, then unscrew and remove the cell.
3. Rinse loose debris out with a hose.
4. In a plastic bucket, add acid to water (never the reverse) at your maker's ratio (table below), outdoors, wearing goggles and gloves.
5. Stand the cell on its cleaning stand or cap. Fill it until the plates are covered but the electrical connection is not.
6. Let it fizz until bubbling stops, usually a few minutes. Don't leave it overnight.
7. Rinse thoroughly and reinstall.
8. Dispose of the spent solution per your manual. Common practice is to pour it slowly into the pool with the pump running, where it acts as pH-down, or to neutralize it with baking soda first.

How much · basis: label (maker ratios) + stoichiometry (strength equivalents)

A 4:1 mix of 31.45% acid is about 7% HCl. One mixed batch, typically ½–1 gal, does one cell.

Cautions:

• Your cell's manual wins. Some makers sell their own milder cleaner.
• Never soak the terminal end.
• Frequent scaling means CSI is too high. Lower pH, TA, or CH rather than washing more often.

Effect & benefit: Strips a very thin layer of plaster, taking embedded stains, scale, and algae shadows with it, and restores a white surface. It's a last resort before replastering. Every wash removes plaster and shortens surface life.

How to use:

1. Drain the pool, following local discharge rules and hydrostatic-pressure precautions. An empty pool can float out of the ground where groundwater is high.
2. Gear: goggles, a respirator with acid-gas cartridges, chemical gloves, and rubber boots. Wet the deck and plants, and work in sections from the top down.
3. Mix the acid solution in a plastic watering can, acid into water.
4. Wet a section with a hose. Pour the acid solution from the top down, scrub immediately with a stiff brush, and rinse within ~30 s, before the plaster turns yellow-gray.
5. The runoff collects in the deep end. Neutralize it with soda ash until fizzing stops and pH is near 7, then pump it out per local rules.
6. Rinse everything twice, then refill and do a new-plaster-style start-up (F1 · L1).

How much · basis: rule of thumb (mix) + stoichiometry (neutralizer)

Cautions:

• ⛔ Not for vinyl, fiberglass, painted, or pebble/quartz finishes without the finish maker's approval.
• Hire a pro if you're unsure. Fumes are strong in an enclosed pool shell.

Effect & benefit: Water with a negative saturation index slowly dissolves calcium carbonate scale. Holding CSI around −0.3 to −0.5 for weeks while you brush the scaled areas wears scale off tile lines and plaster without draining. It works on white, crusty calcium carbonate. Glassy calcium-silicate scale doesn't respond, so test with vinegar first (§4 stain diagram).

How to use:

1. Calculate CSI (§1.6).
2. Lower TA to ~50–60 with acid + aeration (L2), then hold pH at 7.0–7.2. Leave CH where it is.
3. Recalculate CSI. Aim for −0.3 to −0.5. Don't go lower.
4. Brush the scale daily with a stiff brush. Use a pumice stone on tile if the tile maker allows.
5. Retest pH every day or two and re-add acid. Recheck CSI weekly.
6. When the scale is gone, raise TA and pH back to normal (baking soda, aeration) and return CSI to −0.3…+0.3.

How much (per 10,000 gal) · basis: stoichiometry (acid) + model (CSI) + rule of thumb (target)

Taking TA from 80 to 50 takes 2.40 qt (77 fl oz) of 31.45% acid (see the dose card for other strengths). Small daily top-ups then hold pH.

Cautions:

• Aggressive water attacks plaster and grout too. Stop as soon as the scale is gone.
• Low pH speeds corrosion of copper heat exchangers, ladder anchors, and light niches. Bypass or turn off the heater.
• Keep FC on target.

Effect & benefit: Calcium and mineral deposits blind filter fabric, raising pressure and shortening run times. A dilute acid soak dissolves them. Do it only after degreasing: acid on an oily element "sets" the oils into the fabric.

How to use:

1. Degrease first with a filter cleaner or TSP soak (L3), then rinse thoroughly. Never combine the cleaner and the acid.
2. In a plastic trash can, add acid to water at the ratio below, outdoors, wearing goggles and gloves.
3. Soak the element until fizzing stops, usually under an hour.
4. Rinse very thoroughly.
5. Neutralize the leftover soak with baking soda until fizzing stops before disposal.

How much (per soak, not per pool) · basis: rule of thumb

Cautions:

• Check the filter maker's guidance; some discourage acid on certain fabrics.
• Never acid-soak an element that hasn't been degreased.

Effect & benefit: Hardware-store muriatic acid is sold for masonry work. It dissolves the white efflorescence bloom and mortar haze on brick, stone, and concrete, lightens some rust stains, and etches smooth concrete so sealers and paint bond.

How to use:

1. Test a hidden spot first. Acid can lighten or etch colored concrete, and it damages marble, limestone, and travertine. Don't use it on those.
2. Wet the surface and nearby plants with plain water first, so the acid stays on the surface.
3. Apply the dilute solution with a plastic watering can or sprayer. Scrub with a stiff nylon brush.
4. Rinse thoroughly. Then neutralize with a baking-soda wash and rinse again.
5. Keep runoff out of the pool and storm drains.

How much (per gallon of water, not per pool) · basis: label (masonry use) + rule of thumb

Cautions:

• The bottle's own masonry directions win.
• Acid fumes corrode nearby metal, hardware, and pool equipment.
• ⛔ Not on natural stone.

Effect & benefit: The same job as muriatic acid in a granular, no-fume form. It's easier to store, carry, and measure for small spa doses.

How to use:

1. Test pH and TA.
2. Dissolve the dose in a bucket of pool water, adding the granules to the water. Or broadcast it over the deep end with the pump running. Don't let granules sit on vinyl or plaster.
3. Circulate 30–60 min and retest.

How much (per 10,000 gal; TA 80, CYA 40) · basis: model

For a 400-gal spa, multiply by 0.04. For example, 7.8 → 7.4 is ≈ 0.65 oz (18 g).

Cautions:

• Sulfate builds up with every dose. In plaster pools, long-term heavy use is better done with muriatic acid (§1.2).

Effect & benefit: Removes alkalinity using the acid + aeration cycle in E1 · L2.

How to use: Follow E1 · L2. Lower pH to 7.0–7.2 with dry acid, aerate back up, and repeat.

How much (per 10,000 gal) · basis: stoichiometry

See the dose card: 2.15 lb per 10 ppm TA. Taking TA from 120 to 80 takes 8.59 lb, which also adds ≈ 82 ppm sulfate.

Cautions: At large TA reductions, the sulfate load argues for muriatic acid instead.

Effect & benefit: Sodium bisulfate is the active ingredient in some powdered toilet-bowl cleaners. Pool dry acid dissolves the same mineral rings and rust stains in bowls, and lifts hard-water spots from glass and tile.

How to use:

1. Toilet: sprinkle into the bowl, wait 15–30 min, brush, and flush.
2. Tile or glass spots: dissolve in warm water, wipe on, wait a few minutes, wipe off, and rinse.
3. Never use it with bleach or a bleach-containing cleaner in the same bowl or bucket.

How much (per use, not per pool) · basis: rule of thumb

Cautions:

• ⛔ Never combine with bleach: chlorine gas.
• Wear gloves (pH ~1).
• Not for marble or other natural stone.

Effect & benefit: A metered acid feed, controlled by a pH controller, holds pH automatically at large pools. Pool-grade 35–40% sulfuric acid fumes far less than muriatic acid, which spares equipment rooms from corrosion.

How to use:

1. Use only in a chemical feed system designed for sulfuric acid, with containment, and under the facility's health code and the controller maker's setup.
2. Calibrate the pH probe and set feed limits.
3. Track sulfate monthly in plaster pools.

How much (per 10,000 gal; TA 80, CYA 40) · basis: model

For other strengths, scale by the dose card's last column.

Cautions:

• Sulfate accumulates, and high sulfate can degrade cementitious surfaces over years. Dilute periodically.
• 93% concentrate is an industrial chemical: never handle it at home.

Effect & benefit: Where TA is already low and every acid dose would drive it lower, CO₂ lowers pH while leaving TA alone. It has no fumes and adds no chloride or sulfate.

How to use:

1. Install a CO₂ feed system (cylinder or bulk tank, regulator, solenoid, diffuser or injector) per the maker and local code.
2. Control it with a calibrated pH controller.
3. Watch TA. In hypochlorite-fed pools, TA tends to creep up on CO₂ because the base in bleach or cal-hypo is never neutralized (Orenda). Occasional mineral-acid doses rebalance it.

How much (per 10,000 gal) · basis: model

See the dose card. The controller meters the actual feed.

Cautions:

• CO₂ displaces oxygen in closed rooms. Use leak alarms and ventilation.
• Keeping pH low with CO₂ while TA is high adds dissolved CO₂ that keeps outgassing, so feed continues indefinitely.

Effect & benefit: Low pH (below 7.2) stings eyes, corrodes metal (heater, rails, light niches), and etches plaster and grout. Soda ash brings pH up fast and also raises TA, which is exactly what you want when both are low.

How to use:

1. Test pH, TA, and CH. If TA is in range and only pH is low, aerate first. It's free and doesn't raise TA. Borax (E8) is the next-best option, with half the TA increase.
2. Pre-dissolve ~75% of the dose in a bucket of pool water.
3. Pour it slowly around the deep end in front of a return with the pump running. In high-CH water, add it in smaller portions so it doesn't cloud.
4. Circulate at least 1 h, retest, and finish.

How much (per 10,000 gal) · basis: model

Use the dose card. As a quick rule, ~8 oz per 0.2 pH near pH 7.4–7.6 at TA 80. Higher TA, CYA, or borates need more.

Cautions:

• Raises TA about twice as much as borax for the same pH change (TFP; matches the model).
• Overshooting pH above 7.8 risks cloudiness and scale. Fix it with acid (E1).

Effect & benefit: When CH is too high and draining won't help (hard fill water, water restrictions, high water costs), soda ash can pull calcium out of the water. Its carbonate combines with dissolved calcium to form insoluble calcium carbonate, which turns the pool milky. You then remove that solid physically. Done right, it can drop CH by hundreds of ppm in days.

Na2CO3  +  Ca2+  →  CaCO3 (solid)  +  2 Na+
1.06 lb soda ash  →  up to 1.0 lb CaCO3  →  ≈ 12 ppm CH removed per 10,000 gal

Because the carbonate leaves with the calcium, TA ends up roughly where it started once the solid is removed. Sodium takes calcium's place, so TDS barely moves.

A peer-reviewed field case (Hales, Latta & Skinner, JSPSI 6(2), 2023):

• CH ~1,200 → ~600 ppm, using 70 lb of soda ash added in two rounds (20 lb, then 50 lb).
• ~70 lb of precipitate was removed by cleaning the filter every day for 3 days.
• Afterward: TA −20, pH −0.7, saturation index (LSI) from +1.4 to +0.4.

Orenda describes the same chemistry but "does not often recommend" it. It's laborious, and every ounce of precipitate has to come out.

How to use:

1. Confirm the need. Test CH, TA, pH, CYA, and metals, and calculate CSI (§1.6). Most plaster pools are happy at CH 200–400.
2. Check the alternatives first. A partial drain and refill is simpler if your fill water is softer. Fraction to replace = (current − target) ÷ (current − fill water); for example, CH 800 → 400 with 100 ppm fill water means replacing 57%. A mobile reverse-osmosis (RO) service lowers CH, CYA, and TDS without wasting most of the water.
3. Prepare.
   • Turn off the SWG cell and heater (scale), and remove robotic cleaners.
   • Clean the filter. For a sand filter, set up vacuum-to-waste.
   • Raise FC to target. Chlorine is weak at the high pH ahead, so don't let it lapse.
4. Dose one round. Add about 10 lb per 10,000 gal, scaled to the table below. Pre-dissolve it or broadcast it in one area with the pump running; concentrated local addition is what makes the pool "milk" (JSPSI). Expect pH to spike to ~9.5–10.
5. Let it form, then remove it.
   • Sand filter: pump off overnight so the precipitate settles, then vacuum it to waste.
   • Cartridge or DE: keep filtering and clean the filter daily until clear (the JSPSI case took 3 days). A clarifier or floc (H1, H3) speeds clearing.
6. Brush walls and floor daily so settled precipitate can't bond into scale.
7. Retest CH once the water is clear. Repeat rounds until you reach target.
8. Only after the solid is out, lower pH to 7.4–7.6 with acid (E1). Acid added while precipitate is still in the water re-dissolves it and puts the calcium back.
9. Rebalance TA and CSI, then restart the SWG and heater.

How much — model results per 10,000 gal (start pH 7.6, CYA 40, anhydrous soda ash) · basis: model (best case Ω = 1, equilibrium; "realistic" Ω = 20, precipitation stalls while still supersaturated)

• Rule of thumb: each pound of soda ash per 10,000 gal removes up to ~11 ppm CH (theory: 11.3), and ~8–10 ppm in practice. Budget roughly 10 lb per 100 ppm.
• Other forms: monohydrate ×1.16 by weight; decahydrate (sal soda) ×2.69.
• Real results depend on how much of the precipitate you actually remove.

Cautions:

• No swimming until the solid is removed and pH is back to normal. pH 9.5–10+ irritates skin and eyes, and chlorine is nearly inactive.
• Precipitate can scale surfaces and equipment. Brush daily. Keep the SWG cell and heater off. On vinyl and fiberglass, vacuum promptly so it doesn't leave a rough film.
• Copper and iron tend to co-precipitate (a bonus), but brush them up before they stain.
• Hard fill water brings CH back with every top-off. Plan for it.

Effect & benefit: A strong, cheap base that turns spilled or spent muriatic acid into salt water, CO₂, and a little sodium. It's the standard neutralizer for acid-wash runoff (see E1 · O2).

How to use:

1. Wear goggles and gloves. Keep people and pets away, and ventilate.
2. Contain the spill with sand, kitty litter, or a dike of soda ash.
3. Sprinkle soda ash slowly from the edges inward. It fizzes hard, so go slowly.
4. Continue until fizzing stops. Check with pH paper: you want 6–8.
5. Hose down with plenty of water, or scoop up and dispose of per local rules.

How much (per gallon of acid spilled or used) · basis: stoichiometry

Cautions:

• Excess soda ash is itself caustic (pH ~11). Baking soda can't overshoot past pH ~8.3, so it's the safer choice for spills on skin-contact surfaces.
• Neutralize slowly to avoid foaming over.

Effect & benefit: Fiber-reactive dyes (Procion MX type) bond permanently to cotton only at high pH. Pre-soaking fabric in a soda-ash solution makes colors vivid and wash-fast. Dye suppliers sell "soda ash fixer", which is the same chemical as pool pH Up.

How to use:

1. Dissolve the soda ash in warm water.
2. Soak the 100% cotton (or other plant-fiber) items 15–20 min.
3. Wring them out, tie, and dye.
4. Let them sit 6–24 h in a warm place, then rinse cold and wash hot.
5. Use pure sodium carbonate only: no laundry detergent blends, no pool products with additives.

How much (per gallon of water, not per pool) · basis: rule of thumb (dye-supplier directions)

Cautions:

• Wear gloves; the solution is pH ~11.
• Not for wool or silk, which are damaged by high pH.

Effect & benefit: Softens hard water and boosts detergent on greasy, heavily soiled loads. That's exactly what "washing soda" is sold for, and pool soda ash is the same chemical.

How to use:

1. Add it to the wash with your usual detergent.
2. Dissolve it first in warm water for cold washes.
3. Don't use it on wool, silk, or delicate dyes.

How much (per load, not per pool) · basis: label (washing soda)

Cautions:

• Alkaline: avoid contact with eyes.
• Can fade some dyes and leave residue in very hard water.

Effect & benefit: Low TA lets pH swing with every dose of chlorine or acid. Raising TA stabilizes pH, protects plaster and metal, and is the standard fix after tablets or acid have eaten the alkalinity.

How to use:

1. Test TA and pH. If pH is low and TA is low, add baking soda first, then retest pH.
2. Broadcast it over the deep end, or pre-dissolve it, with the pump running.
3. Add no more than ~10 lb per 10,000 gal at a time. Very large doses can cloud the water briefly.
4. Retest TA after ~6 h of circulation.

How much (per 10,000 gal) · basis: stoichiometry

Use the dose card: 1.4 lb per 10 ppm. For a 400-gal spa, it's ≈ 0.9 oz per 10 ppm.

Cautions:

• It won't raise pH much. If pH also needs to climb, use aeration, borax, or a little soda ash afterward.
• Don't overshoot. Lowering TA again takes acid plus aeration (E1 · L2).

Effect & benefit: Fresh plaster leaches calcium hydroxide into new water. That can dust, discolor, or weaken the surface.

• NPC's traditional start-up brings TA, pH, and CH up over several days while brushing.
• The "bicarb start-up" (onBalance, not endorsed by NPC) instead fills the pool with water so saturated with bicarbonate that the plaster has little reason to leach. Proponents use it to avoid days of brushing.

Follow your plasterer's method. Warranties often specify one.

How to use (bicarb start, onBalance):

1. Test the fill water's TA and CH.
2. Calculate the bicarbonate to add (formula below). Targets: TA ≥ 120, TA + CH ≥ 400, LSI ≈ +1.0.
3. Dissolve the bicarbonate in a drum or bin that the incoming fill water runs through, so the first water touching the plaster is already saturated.
4. After filling, add acid to bring pH to 7.7–7.9.
5. Keep TA high and pH ≤ 8.2 for the first month. Then step down to normal balance.

For comparison, NPC's traditional start-up (2021 card):

How much · basis: label (onBalance formula) + stoichiometry

Bicarbonate to add, ppm (as TA) = 500 − (fill TA + fill CH). Pounds = gallons ÷ 71,400 × that ppm, which is the same as 1.40 lb per 10 ppm per 10k gal.

Cautions:

• Not NPC-endorsed.
• High TA makes pH climb, so watch it daily the first month.
• Never add calcium chloride and bicarbonate at the same time.
• No SWG salt for 30 days on new plaster (NPC).

Effect & benefit: Baking soda neutralizes acid spills and splashes but can't overshoot into caustic territory (it tops out at pH ~8.3). It's the safer choice near skin, decks, and plants. Keep an open box near where you handle acid.

How to use:

1. Wear goggles and gloves.
2. Pour baking soda over the spill, starting at the edges, until fizzing stops.
3. Check with pH paper, then rinse with plenty of water.
4. For acid on skin, flush with water first for 15 minutes. Don't rub baking soda into a burn.

How much (per gallon of acid) · basis: stoichiometry

Cautions:

• It foams a lot. Go slowly so it doesn't overflow the containment.

Effect & benefit: A mild, non-scratching abrasive. A baking-soda paste lifts the greasy "bathtub ring" of sunscreen and body oils at the waterline without scratching vinyl or gelcoat, and anything that falls in only nudges TA up.

How to use:

1. Mix the paste.
2. Rub it onto the scum line with a soft sponge or microfiber cloth.
3. Rinse the area with pool water.
4. For heavy oil, follow with an enzyme product (K1).

How much (per batch, not per pool) · basis: rule of thumb

Cautions:

• It won't remove calcium scale. For that, use E1 · O3 or I2.

Effect & benefit: Heated baking soda releases CO₂ and helps smother a small stovetop grease fire. Water makes grease fires explode, and flour can ignite. A box near the stove (or a pool-supply bucket near the grill) is cheap insurance.

How to use:

1. Turn off the heat. Don't carry the pan.
2. First choice: slide a metal lid or a baking sheet over the pan.
3. If you have no lid and the fire is small, dump baking soda generously over it.
4. If the fire isn't out within seconds, or it's bigger than the pan, get out and call 911. Use a Class K or B extinguisher if you're trained.

How much (per fire) · basis: rule of thumb

Enough to cover the burning surface: several cups for a skillet. A 1-lb box is the minimum to keep at the stove.

Cautions:

• ⛔ Never water on grease. ⛔ Never flour.
• Not for oven, electrical, or large fires.

Effect & benefit: A liquid base that a metering pump can feed under pH-controller control. It's used where acid feeds, CO₂, or trichlor drive pH down. Compared with soda ash it adds about half the TA per pH unit and dissolves instantly.

How to use:

1. Use only in a feed system rated for caustic, with secondary containment and the controller maker's setup, under the facility's code.
2. Calibrate the pH probe. Set feed limits so a stuck probe can't overdose.

How much (per 10,000 gal) · basis: model

See the dose card. In practice the controller meters the feed.

Cautions:

• 25–50% caustic causes deep chemical burns and blindness within seconds. Use a face shield, goggles, gloves, and an apron, and have an eyewash station on site.
• Freezing and crystallization: 50% caustic solidifies below ~55 °F.

Effect & benefit: When both CH and TA are too high, sodium hydroxide raises pH so that calcium precipitates using the bicarbonate already in the water:

Ca2+ + HCO3- + OH-  →  CaCO3 (solid) + H2O

This is the chemistry of municipal lime softening. Each 100 ppm of CH removed also removes about 50 ppm of TA (net), so one treatment fixes both numbers. Soda ash (E5 · O1) lowers CH but leaves TA roughly where it was.

How to use:

1. Do this only if TA is well above target (≥ 120) and CH is too high. Otherwise TA will crash; use soda ash instead.
2. Follow every preparation and removal step of E5 · O1: SWG and heater off, FC at target, settle or filter, brush, and remove the precipitate before any acid.
3. Wear a face shield, goggles, gloves, and an apron.
4. Add the 50% caustic very slowly, low, in front of a return in the deep end with the pump running, so it disperses before reaching any surface. Never pour it near people, pets, or the skimmer.
5. Retest CH and TA once the water clears. Repeat a smaller round if needed. Bring pH back with acid only after the precipitate is gone.

How much — model results per 10,000 gal (start pH 7.6, CYA 40) · basis: model (best case Ω = 1; realistic Ω = 10)

With 25% caustic, use 2.4× the volume. Very roughly, each 32 fl oz of 50% per 10k gal removes ~35–60 ppm CH and ~20–30 ppm TA, more in very hard, high-TA water.

Cautions:

• This is the most hazardous procedure in this guide. One splash in an eye can blind. If in any doubt, use soda ash.
• No swimming until the precipitate is removed and pH is normal.
• The scale risk to surfaces and equipment is the same as in E5 · O1.

Effect & benefit: Lifts low pH while adding about half the TA that soda ash would (TFP; matches the model). That's useful when pH is low but TA is already fine. TFP's rule: if pH is below 7.0 and TA is at least 50, use borax to bring pH to ~7.4. Each dose also adds a little borate.

How to use:

1. Try aeration first if TA is fine. It raises pH with no chemicals.
2. Pre-dissolve borax in a bucket of warm pool water. It dissolves slowly in cold water.
3. Pour it around the deep end in front of a return, pump running.
4. Circulate 1 h, retest, and finish with the remaining ~25%.

How much (per 10,000 gal) · basis: model

Use the dose card. As a rule of thumb, decahydrate weighs about 2× the soda-ash dose for the same pH change (pentahydrate about 1.5×).

Cautions:

• Each pound of decahydrate adds 1.35 ppm boron. Repeated pH-up use slowly builds borates. Track them if you use borax often.

Effect & benefit: Borates at 30–50 ppm resist the steady pH rise of SWG and aerated pools, so you need less acid between corrections. They also mildly discourage algae, and many people find the water feels "softer". Borax plus muriatic acid gives you borates while the acid cancels borax's pH rise. The net product is boric acid, at a fraction of branded-borate cost.

How to use:

1. Test borates; fresh water is ~0. Pick a target of 30–50 ppm, never above 50 (PHTA).
2. Work in rounds:
   1. Dissolve borax in buckets of warm pool water and pour it in, pump running. pH rises.
   2. Add acid in front of a return to bring pH back to ~7.2–7.4.
   3. Circulate several hours, retest pH, and repeat.
3. TFP's round is about 1 gal of 31.45% acid with ~3½ four-pound boxes (~14 lb) of borax. That adds ≈ 19 ppm B per 10,000 gal per round.
4. Retest borates after the last round. Afterward, acid demand rises near pH 7.5–8, by about 2–3× (§6.2). That's the buffer working.

How much (per 10,000 gal) · basis: stoichiometry (borax + acid) + label (ProTeam)

With ~20% acid, use 1.65× the 31.45% volume. With 14.5% acid, use 2.34×.

Branded borate products, per label:

Cautions:

• Pets: dogs that drink pool water are the main concern. TFP estimates a 100-lb dog would need ~8 L a day of 50 ppm water to reach the no-adverse-effect level, but don't let pets use the pool as their water bowl. EPA's acceptable boron intake is 0.2 mg/kg/day. EPA and NSF reviews found 30–50 mg/L posed no significant risk to swimmers (PHTA).
• Borates are removed only by dilution.

Effect & benefit: 20 Mule Team Borax is sodium tetraborate decahydrate, the same chemical pool-store "pH Plus" borax products contain, and typically far cheaper per pound. With grocery muriatic acid it makes the TFP borate recipe above.

How to use:

1. Check the box: it should list sodium tetraborate (decahydrate) only. No "with detergent" or scented variants.
2. Use it exactly as in L1 (pH up) or L2 (borates).
3. Store opened boxes dry; they cake but still dissolve.

How much (per 10,000 gal) · basis: stoichiometry

Cautions: Same pet and ingestion cautions as L2.

Effect & benefit: Leftover pool borax softens wash water and boosts detergent, the use it's labeled for in the laundry aisle.

How to use:

1. Add it with your detergent.
2. Pre-dissolve it in warm water for cold washes.

How much (per load, not per pool) · basis: label (laundry borax)

½ cup per load.

Cautions:

• Pentahydrate pool borate is stronger per cup; reduce to about ⅓ cup.
• Keep it away from children and pets.

Effect & benefit: The cleanest route to a 30–50 ppm borate buffer (E8 · L2 explains why). No acid juggling is needed, and pH drifts down only a little.

How to use:

1. Test borates and pH. Plan the dose, never exceeding 50 ppm.
2. With the pump running, broadcast boric acid thinly over the deep end. Don't put it in the skimmer: it dissolves slowly (~0.4 lb per gallon of cool water) and can clog baskets.
3. Brush the floor every few hours until the powder is gone, which can take a day or two.
4. Retest pH. Expect ~0.2–0.3 lower. Bring it back with aeration, soda ash, or borax.
5. Retest borates after 24–48 h.

How much (per 10,000 gal) · basis: stoichiometry

Use the dose card. For a 400-gal spa, +30 ppm is ≈ 0.57 lb (9.2 oz).

Cautions:

• Same pet and ingestion cautions as E8.
• Undissolved piles can stain or etch plaster as they sit; brush them out.

Effect & benefit: Branded borate products are boric acid, borax, or blends. A 50-lb bag of technical-grade boric acid from a chemical supplier delivers the same boron, often at a fraction of the price.

How to use:

1. Buy technical-grade (≥ 99.9%) boric acid and confirm "boric acid, CAS 10043-35-3" as the only ingredient on the SDS.
2. Use it exactly as in L1.

How much (per 10,000 gal) · basis: stoichiometry

Cautions:

• ⛔ Don't use insecticide "roach powders" (they may contain dyes or other ingredients).
• ⛔ Never use pool-grade boric acid for eyewash, antiseptic, or any personal-care purpose.
• Keep it labeled and away from food and children.

Effect & benefit: Water short on calcium (CSI well below −0.3) pulls calcium out of plaster, grout, and pebble finishes. That causes etching, roughness, and pitting. Raising CH to the PHTA ideal (200–400 pools, 150–250 spas) protects them and widens the safe pH range.

How to use:

1. Test CH, then calculate CSI (§1.6) and how much CH you need.
2. Fill a clean plastic bucket ¾ with pool water, then add the calcium chloride slowly while stirring. Never add water to the dry product.
   • It gets hot: anhydrous pellets can heat a gallon by ~35 °F per pound (calc).
   • Flake heats less.
   • Do larger amounts in batches.
3. Pour it around the perimeter in front of the returns, pump running. Don't dump undissolved pellets on vinyl or plaster.
4. For big increases, add in portions (NPC: 10-lb increments on new plaster). Never add it on the same day as baking soda or soda ash.
5. Retest after 6–24 h of circulation.

New plaster (NPC start-up card):

See E6 · O1 for the full schedule.

How much (per 10,000 gal) · basis: stoichiometry + label

Use the dose card, then confirm with a CH test.

Cautions:

• Bromide note: OxyChem states that its solid calcium chloride "contains bromide" (amount not given). Bromide turns some chlorine into bromine, which CYA can't protect. If chlorine loss jumps after a very large calcium dose in a sunny pool, suspect this.
• Overshooting CH is fixed only by dilution or precipitation (E5 · O1).
• SWG pools: keep CSI ≤ 0 so the cell doesn't scale.