Pool Chemical Calculator
Calculate the dose that moves a pool reading to its target: chlorine, pH, alkalinity, calcium or stabilizer, scaled from your pool volume in gallons.
By CalcBuilt Editorial TeamUpdated September 9, 2026Formulas checked against manufacturer specs, see how we calculate.
Results
- Amount to add
- 31.5 fl oz
- Liquid chlorine, 12.5% to move free chlorine from 0.5 to 2 ppm in 20,000 gal
- Dosing rate used
- 10.5 fl oz per ppm per 10,000 gal
- Published dose per 10,000 gal, scaled straight to your volume
- How to add it
- See note
- Pour it slowly around the deep end with the pump running. Do not hold the jug in one spot over a vinyl liner
- Retest in
- 4 hours, or one full turnover of the water
- Run the pump the whole time, then test again before adding more. Dose off a fresh test, never off last week's numbers
- Target range check
- 1 to 3 ppm
- Inside the recommended 1 to 3 ppm
Pool Chemical formula
Dose = published amount per 10,000 gal x change needed x (pool gallons / 10,000)
Free chlorine, 1 ppm per 10,000 gal: 10.5 fl oz liquid 12.5%, 2 oz cal-hypo 65%, 2.5 oz dichlor 56%, 1.5 oz trichlor 90%
Alkalinity 10 ppm = 1.4 lb sodium bicarbonate; Calcium 10 ppm = 1.25 lb calcium chloride 77%; Stabilizer 10 ppm = 13 oz
pH: 6 oz soda ash raises 0.2; 12 fl oz muriatic acid 31.45% lowers about 0.2Worked example
A 15,000 gallon pool tests 70 ppm alkalinity and you want 100 ppm. The change is 30 ppm, and sodium bicarbonate moves 10 ppm per 10,000 gallons with 1.4 lb. So 1.4 x 3 x 1.5 = 6.3 lb of baking soda. Split it into two doses a day apart, broadcast with the pump running.
The same pool reads pH 8.0 and you want 7.5. Muriatic acid at 31.45% drops about 0.2 pH per 12 fl oz per 10,000 gallons, so 12 x 2.5 x 1.5 = 45 fl oz. Add about half, run the pump an hour, then retest: high alkalinity buffers the water and eats more acid than the chart predicts.
Quick reference
| Change | Product | Amount |
|---|---|---|
| Free chlorine +1 ppm | Liquid chlorine, 12.5% | 10.5 fl oz |
| Free chlorine +1 ppm | Cal-hypo granules, 65% | 2 oz |
| Free chlorine +1 ppm | Dichlor granules, 56% | 2.5 oz |
| Free chlorine +1 ppm | Trichlor tablets, 90% | 1.5 oz |
| Total alkalinity +10 ppm | Sodium bicarbonate | 1.4 lb |
| Calcium hardness +10 ppm | Calcium chloride, 77% | 1.25 lb |
| Cyanuric acid +10 ppm | Stabilizer | 13 oz |
| pH +0.2 | Soda ash | 6 oz |
| pH -0.2 | Muriatic acid, 31.45% | 12 fl oz |
Test first, then dose in the right order
Every dose here starts from a fresh test, and the order matters. Balance total alkalinity first, because it decides how far pH moves when you touch anything. Then pH, then calcium hardness, then stabilizer, and chlorine last. Chasing pH before alkalinity is the classic way to burn through a case of acid and end up where you started. Use a DPD or FAS-DPD kit for chlorine; strips read total chlorine and drift with age, which is why two strips from the same bottle can disagree by a full ppm.
Test at least twice a week in season, and after heavy rain, a party, or a week over 90 degrees. Cyanuric acid needs checking only monthly, since nothing but dilution moves it. Write the numbers down: a pool that needs acid every week has an alkalinity problem, and a pool that eats chlorine with a good chlorine reading has a stabilizer problem. The dose is only as good as the volume it is scaled to, so measure the pool once and keep the number.
Adding chemicals without wrecking the surface
Run the pump for the entire dose and for hours after. Liquid chlorine goes in slowly around the deep end, never held in one spot over a vinyl liner. Cal-hypo dissolves in a bucket of pool water first on vinyl and fiberglass, then gets broadcast; it also adds about 0.7 ppm of calcium hardness for every ppm of chlorine, which matters in hard-water regions. Dichlor and trichlor carry stabilizer, about 0.9 and 0.6 ppm per ppm of chlorine, so a season of tabs is what pushes cyanuric acid past 90.
Acid deserves respect. Pour muriatic acid slowly into the deep end with the pump running, always acid into water, and never within an hour of a chlorine dose, because the two together give off chlorine gas. Soda ash and calcium chloride both go in a bucket first; calcium chloride heats the bucket, so add flakes to water and stand back. Broadcast sodium bicarbonate over the deep end and expect a few cloudy hours. Then wait: retest chlorine in about 4 hours, pH and alkalinity in 4 to 6, and stabilizer in 2 to 5 days, because the granules take that long to read.
What this calculator leaves out
It does not test the water, and it does not know what your pool has been doing. Not covered: salt for a chlorine generator, about 27 lb per 1,000 gallons to reach 3,200 ppm; algaecide and clarifier; phosphate removers; filter cleaning; and the Langelier saturation index that ties pH, alkalinity, calcium and temperature together on plaster pools. Draining part of a pool to cut stabilizer or hardness is a job with real risk on a high water table, since an empty vinyl or fiberglass shell can float.
Code limits that apply
- CDC healthy swimming, free chlorinechecked
At least 1 ppm, or 2 ppm in a pool holding cyanuric acid; 1 to 3 ppm is the usual residential band
If you miss it: Under 1 ppm the water stops disinfecting and algae takes the walls within a warm week
- CDC MAHC, free chlorine ceilingchecked
Over 10 ppm with swimmers in the water is a closure condition in public pools
If you miss it: Skin and eye irritation and bleached suits; wait it out rather than adding neutralizer by guess
- CDC healthy swimming, pHchecked
7.0 to 7.8, with 7.2 to 7.8 the usual residential band and 7.4 to 7.6 the sweet spot
If you miss it: Under 7.2 the water etches plaster and corrodes heater parts; over 7.8 chlorine goes lazy and scale forms
- Industry practice, total alkalinitychecked
60 to 180 ppm, ideal 80 to 120 ppm
If you miss it: Low alkalinity lets pH bounce after every rain; high alkalinity locks pH up and eats acid
- Industry practice, calcium hardnesschecked
200 to 400 ppm
If you miss it: Under 200 ppm the water pulls calcium out of plaster and grout; over 400 ppm it scales the heater and salt cell
- Industry practice, cyanuric acidchecked
30 to 50 ppm outdoors, never above 90 to 100 ppm
If you miss it: Past 90 ppm chlorine is bound up and tests fine while algae grows; only a partial drain lowers it
- MAHC bather load and turnover
The pump should turn the water over in 8 to 10 hours for chemicals to spread evenly
If you miss it: Dosing a pool that is not circulating leaves a hot layer at one end and untreated water at the other
Rows marked checked produce a warning in the results when an entry crosses the limit. The others are on the plans or on site and this calculator does not test them. Local amendments can be stricter; the adopted edition and the inspector govern.
Mistakes that cost money
- Running trichlor tabs all season: at 0.6 ppm of stabilizer per ppm of chlorine the reading passes 90 ppm by August and only a drain fixes it.
- Cal-hypo dropped in a skimmer that has fed trichlor: the two react violently and can catch fire; broadcast shock across the deep end instead.
- Acid and chlorine added in the same hour release chlorine gas at the plume; leave one full turnover between doses.
- Dosing off an old test strip: strips read total chlorine and drift with age and heat, so a DPD or FAS-DPD test decides the dose.
- Guessing at pool volume: a 20 percent error in gallons is a 20 percent error in every dose you will ever make.
- Muriatic acid poured in one spot with the pump off etches plaster and pits a heater core; pour it slowly into the deep end with the pump running.
Key facts
- Per 10,000 gallons, 1 ppm of free chlorine takes about 10.5 fl oz of 12.5% liquid chlorine or about 2 oz of 65% cal-hypo.
- Sodium bicarbonate raises total alkalinity about 10 ppm per 1.4 lb per 10,000 gallons; 13 oz of stabilizer raises cyanuric acid 10 ppm.
- CDC recommends free chlorine of at least 1 ppm, or 2 ppm in a stabilized pool, with pH from 7.0 to 7.8.
- Trichlor tablets add about 0.6 ppm of cyanuric acid for every 1 ppm of chlorine, and dichlor about 0.9 ppm.
- Nothing lowers alkalinity, calcium hardness or cyanuric acid except draining and refilling with fresh water.
Frequently asked questions
How much chlorine do I add to a 20,000 gallon pool?
To raise free chlorine 1 ppm, about 21 fl oz of 12.5% liquid chlorine or about 4 oz of 65% cal-hypo. Going from 0.5 to 2 ppm takes 1.5 times that, which is 31.5 fl oz of liquid chlorine.
How much baking soda raises alkalinity?
About 1.4 lb of sodium bicarbonate per 10 ppm per 10,000 gallons. A 20,000 gallon pool going from 70 to 100 ppm needs about 8.4 lb, best split into two doses a day apart.
How do I lower cyanuric acid?
By draining and refilling. Nothing you add removes stabilizer, so dropping 100 ppm to 50 ppm means replacing about half the water. Stop using trichlor tabs and dichlor first, or it climbs right back.
How long after adding chemicals can we swim?
Once free chlorine is back between 1 and 3 ppm and pH is 7.2 to 7.8, usually 4 hours with the pump running after a routine dose. After a heavy shock, wait until free chlorine falls below 5 ppm and test before anyone gets in.
Sources and references
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Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.