EstimatorKitFree pool chemical calculator
Pool doses in the order they go in
Type the pool’s gallons and the five readings off your test kit — free chlorine, pH, total alkalinity, calcium hardness and cyanuric acid — and this returns a numbered sequence rather than five loose numbers: what to add first, how much of the product you actually own, what that product drags into the other four readings, and how long to wait before the next retest counts. Rates come from each compound’s own assay, since one part per million in 10,000 gallons is 1.34 ounces of material and every dose on the page is that figure divided by what is in the bag.
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- 5 readings
- Doses per 10,000 gal
- Retest interval on each
Doses are written per 10,000 gallons, so this is the multiplier on all five. The pool volume calculator weights a sloping floor properly instead of averaging the two ends.
| Reading | Tested | Target | Ideal |
|---|---|---|---|
| Total alkalinity | 80–120 | ||
| pH | 7.4–7.6 | ||
| Calcium hardness | 200–400 | ||
| Cyanuric acid | 30–50 | ||
| Free chlorine | 2–4 |
Ideal columns are the ideal and acceptable columns of a residential test-kit card, which follow the ANSI/APSP/ICC-11 water-quality standard. The acceptable range is wider than the ideal one on every row — alkalinity to 180, hardness to 1000 — so a reading just outside the band is a note, not an emergency.
Which products are in your shed
The assay on your own label beats every figure here. A 65% cal hypo, an anhydrous dichlor and a jug of liquid chlorine that has spent a month in the sun all dose differently from the products named above.
4 of the five need a product
48 fl oz (1.5 qt) · 16.2 lb · 1.88 lb · 30.7 fl oz
Worked in the order below and not in any other. Each one moves at least one of the others, so a dose calculated from readings taken before the previous step landed is a dose calculated from a pool that no longer exists.
1. Total alkalinity — bring it down first
48 fl oz (1.5 qt) Muriatic 31.45%
130 down to 100 ppm takes 115 fl oz (3.59 qt) in total, split across additions. This is the first one.
Rate: 38.3 fl oz (1.2 qt) per 10 ppm in this pool, from full-strength 20° Baumé muriatic acid, 31.45% hydrogen chloride at 1.16 g/mL: one equivalent of acid destroys 50 g of alkalinity measured as calcium carbonate.
Costs: Takes pH down at the same time — the same bottle does both, which is why they are never dosed separately. The addition is capped at the largest single addition of 31.45% muriatic acid handled as routine: a quart per 10,000 gallons, poured slowly, then circulated and retested before any more.
Handling: Pour slowly into the deepest water with the pump running, as far from the skimmer as the pool allows. Acid and any chlorine product must never meet outside the pool.
Then: 30 minutes of circulation, then retest pH and alkalinity together.
2. pH — already covered by step 1
nothing yet
pH 7.9 against a target of 7.5, but the acid above is aimed at both readings. Adding a second dose for pH on top of it is how a pool ends up at 7.0 with the alkalinity stripped out.
Then: Retest pH and alkalinity together after the acid has circulated, then recalculate.
3. Calcium hardness — top it up
16.2 lb Calcium chloride 94%
190 up to 300 ppm. Soft water is not gentle water: it pulls calcium out of whatever it can reach, which on a plaster or pebble finish is the finish itself, and on a heater is the exchanger.
Rate: 1.48 lb per 10 ppm in this pool, from anhydrous calcium chloride flake, 94% CaCl₂.
Costs: Nothing else moves — but note that chlorinating with cal hypo adds 0.71 ppm of hardness for every ppm of chlorine, so this reading climbs on its own if that is your shock.
Handling: Dissolve in a bucket of water first and add the calcium to the water, never the water to the calcium — the reaction gets hot enough to matter.
Then: 6 hours, and retest before adding a second lot.
4. Cyanuric acid — stabilize before the chlorine goes in
1.88 lb granular cyanuric acid
25 up to 40 ppm. Unstabilized chlorine in full sun is half gone in well under an hour; stabilizer holds it there. This step comes before the chlorine step because it changes what the chlorine target has to be.
Rate: 1.25 lb per 10 ppm in this pool. Cyanuric acid is sold essentially pure, so the dose is the ppm mass itself with nothing to divide by.
Costs: Raises the chlorine you have to carry: at 40 ppm the working floor is about 3 ppm of free chlorine.
Handling: In a sock in the skimmer basket or the pump strainer, squeezed once a day. Do not backwash for two days afterwards or you flush out what has not dissolved yet.
Then: 5 to 7 days. It is the slowest-dissolving thing in the shed and the reading lies until it has gone in.
5. Free chlorine — last, because the four above set its target
30.7 fl oz Liquid chlorine 12.5%
1 up to 3 ppm.
Rate: 15.4 fl oz per ppm in this pool — sodium hypochlorite sold by trade percent — grams of available chlorine per 100 mL, which is why one gallon in 10,000 gallons raises free chlorine by the trade number itself in ppm.
Costs: Adds no calcium and no stabilizer, which is the whole reason it stays the default on a pool that already has both.
Handling: Pour over a return with the pump running. Strength falls with age, heat and light, so a jug that has stood in a hot shed all July doses short of its label.
Then: One full turnover of the pump — the time it takes to move the whole volume once — before a reading counts.
One product at a time, each poured into water the pump is already moving, and never two within an hour of each other. Acid and any chlorine product meeting outside the pool — in a bucket, a scoop or a shelf that leaks — is the accident that puts pool owners in hospital, and cal hypo with trichlor is the one that starts fires. A pool that has already gone cloudy or green is past what a dosing page can settle: the salt page carries the swap arithmetic for the two readings only water can lower, and the label on the bottle in your hand outranks every number above it.
How to work out pool chemical doses
Three steps, and the discipline is entirely in the third.
Test all five before dosing any of them
Free chlorine, pH, total alkalinity, calcium hardness and cyanuric acid, from the same sample, taken elbow-deep away from a return and a skimmer. Five readings are needed for one dose because the readings are not independent: the chlorine figure that is right at 25 ppm of stabilizer is wrong at 80, and the acid that fixes pH is the same bottle that decides alkalinity.
Enter the volume and let the order fall out
Everything is written per 10,000 gallons, so the volume is the multiplier on all five doses at once. The tool returns them as a numbered sequence with alkalinity at the top, because it is the buffer that determines how far pH moves for any given dose, and any pH work done before it is set has to be redone afterwards.
One product, one wait, one retest
Take the first line only. Pour it into water the pump is already moving, wait the interval printed against it — half an hour for acid, six hours for a dry alkalinity or calcium adjustment, a full turnover for chlorine, most of a week for stabilizer — and retest before calculating anything else. Doses stacked inside one afternoon are doses calculated from a pool that has already changed.
Technical specifications
| Dose basis | 1 ppm in 10,000 US gallons is 37.85 g of material — 1.34 oz — and every rate below is that figure divided by the product's own assay |
|---|---|
| Sequence | Alkalinity, pH, calcium hardness, cyanuric acid, free chlorine, with a retest interval printed against each |
| Alkalinity up | 1.4 lb of sodium bicarbonate per 10 ppm per 10,000 gallons, from its molar weight against the 50.04 g equivalent alkalinity is measured in |
| Alkalinity down | 25.6 fl oz of 31.45% muriatic acid per 10 ppm per 10,000 gallons, capped at one quart per 10,000 gallons in a single addition |
| Chlorine | Liquid at 10.2 fl oz per ppm, cal hypo 73% at 1.83 oz per ppm, dichlor 56% at 2.38 oz per ppm, all per 10,000 gallons |
| Carried in with it | Cal hypo adds 0.71 ppm of hardness per ppm of chlorine; dichlor adds 0.90 ppm of stabilizer; trichlor adds 0.62 ppm |
| Hardness and stabilizer | 0.98 lb of 94% calcium chloride per 10 ppm, 13.4 oz of cyanuric acid per 10 ppm, per 10,000 gallons |
| Stored or sent | Nothing — readings are typed, multiplied and discarded |
Frequently asked questions
What order should pool chemicals be added in?
Total alkalinity, then pH, then calcium hardness, then cyanuric acid, then free chlorine. Alkalinity leads because it is the buffer: at 60 ppm a pool's pH swings on a small dose and at 140 it barely moves, so setting pH first means setting it against a curve you are about to change. Chlorine comes last because the four readings above it decide what its target has to be, and stabilizer sits just before it because a week-long dissolve has to be under way before the chlorine number means anything.
Why does lowering pH also lower total alkalinity?
Because acid does not act on pH directly — it destroys carbonate alkalinity, and pH falls as a consequence. One equivalent of hydrochloric acid neutralizes 50 g of alkalinity measured as calcium carbonate, which is why 25.6 fluid ounces of 31.45% muriatic acid takes exactly 10 ppm out of 10,000 gallons no matter what the pH reading was when you started. The pool then breathes carbon dioxide back out and pH climbs part of the way home while the alkalinity stays gone, which is the mechanism behind a summer of chasing pH and finding alkalinity at 50 in September.
How do I lower alkalinity without lowering pH?
Acid, then air. There is no product that separates the two, so the standard routine deliberately overshoots on pH and then walks it back: add the acid, which drops both, and then aerate — point a return jet upward, run a spillover, open a water feature — which drives off carbon dioxide and raises pH while leaving alkalinity where the acid put it. It takes hours rather than minutes, and it is the one adjustment on this page whose second half costs nothing at all.
How much liquid chlorine does 10,000 gallons need?
One gallon raises 10,000 gallons by the trade percentage printed on the jug, in ppm. That is not a coincidence — trade percent is defined as grams of available chlorine per 100 mL, and the arithmetic works out so that 12.5% product gives 12.5 ppm, 10% gives 10 ppm, and a single ppm costs 10.2 fluid ounces of the 12.5%. Household bleach is labeled the other way, by weight, so an 8.25% jug is nearer 9.2 ppm per gallon and the two labels are not interchangeable.
What does too much cyanuric acid do to chlorine?
It binds most of it into a reserve, so the test strip keeps reading 3 ppm while almost none of the chlorine is available to kill anything. The working floor scales with the stabilizer reading rather than sitting at a fixed number — around 7.5% of it — so a pool at 100 ppm of cyanuric acid needs about 7.5 ppm of free chlorine to do the job 2 ppm does at 25. Nothing takes stabilizer out except replacement water, and the CDC's Model Aquatic Health Code caps it at 90 ppm for exactly this reason.
Why is my calcium hardness rising when I never added calcium?
Two sources, and the first surprises people. Calcium hypochlorite shock is 28% calcium by weight, which works out at about 0.71 ppm of hardness for every 1 ppm of free chlorine it delivers — so a season of shocking a 15,000 gallon pool with cal hypo puts hundreds of ppm in without anything being spilled. The second is the hose: hard fill water carries its own calcium, and every gallon lost to evaporation and replaced leaves that calcium behind. Neither can be reversed except by swapping water out.
About dosing five readings that all move each other
Almost every dosing page treats pool water as five independent problems with five independent answers, and that is the error the whole design of this one is arranged around. The readings are coupled. Acid lowers pH and alkalinity from the same bottle. Sodium bicarbonate raises both. Calcium hypochlorite hands you 0.71 ppm of hardness for every ppm of chlorine, dichlor hands you 0.90 ppm of stabilizer for the same ppm, and trichlor tablets hand you 0.62 — none of which can be taken back out. So a page that gives you five numbers to act on gives you five numbers that were all calculated from a pool that stops existing the moment you act on the first one. The output here is a sequence with an interval against every line, and the intervals are not padding: acid needs half an hour of circulation, a dry alkalinity or calcium adjustment needs six, chlorine needs a full turnover of the pump, and granular cyanuric acid needs most of a week in a sock before the reading it produces is real.
The one dose this page will not invent is pH. A strong acid’s quantity is fixed by the alkalinity it destroys — one equivalent neutralizes 50.04 grams measured as calcium carbonate, which is arithmetic — but how far pH falls for that quantity depends on where the water sits on its buffer curve and on how fast it outgasses carbon dioxide afterwards, which is not. That is what an acid-demand titration in a drop kit measures and what a pH reading alone cannot tell you. So acid here is dosed by the alkalinity you intend to remove, capped at a quart per 10,000 gallons in one addition, and the pH movement is reported as something to retest rather than predicted. It is also why the classic trick works: add acid to drop alkalinity on purpose, then aerate to walk pH back up, since blowing off carbon dioxide raises pH and leaves alkalinity alone. Aeration is the only adjustment on the page that adds nothing to the water at all.
Two things sit outside this tool by design. The volume is one — every rate here is per 10,000 gallons, so a capacity that is 5% high makes every dose below it 5% strong, every time, for as many seasons as the figure goes unchecked — worth ten minutes with a tape on the pool volume calculator rather than a guess. Salt is the other: a chlorinator’s salt level is a separate reading with a separate failure mode and its own page, the pool salt calculator, which also carries the proportional water-swap arithmetic that is the only cure for the two readings here — stabilizer and hardness — that nothing removes. And if the water you are treating turns out to be a liner over a dug hole with fish in it, stop: pond treatments are dosed per 1,000 gallons against a completely different tolerance, and the pond volume calculator is the one that speaks in those units.
Test results are not a record we keep
Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — measurements, quantities, the prices your supplier quoted you — is uploaded, logged or kept, which is also why the calculators carry on working on a site with no signal.
The five readings you type are multiplied and thrown away when the tab closes. There is no history, no trend line and no account, which means the page cannot tell you what changed since last week — a paper log by the test kit still beats it at that, and it is the one thing worth keeping.