Pool Chemical Calculator (Chlorine, Alkalinity, CYA, Calcium, Salt)
On this page
Enter your pool volume, what your test kit reads now, and the level you want. The calculator works out the dose from the chemistry and the product strength, so it is not tied to one brand or to a 10,000-gallon pool.
Safety first
Pool chemicals can start fires or release toxic gas when they are handled wrong. Virginia's Department of Health gives these rules (VDH):
- Only mix chemicals as the label directs. Never combine old and new product, even when the labels match.
- Add chemicals to water, never water to chemicals.
- Never store liquid chemicals above dry chemicals, and keep everything in its original container.
- Wear the protective gear the label lists, such as goggles and gloves.
How the calculator works
ppm means milligrams per liter, so every dose starts from the pool's volume in liters: gallons × 3.785. Then:
| Change | Grams of active ingredient |
|---|---|
| Free chlorine +X ppm | liters × X ÷ 1,000 (as available chlorine) |
| Total alkalinity +X ppm, with baking soda | liters × X × 84.0 ÷ 50.0 ÷ 1,000 |
| Cyanuric acid +X ppm | liters × X ÷ 1,000 |
| Calcium hardness +X ppm, with calcium chloride | liters × X × 111.0 ÷ 100.1 ÷ 1,000 |
| Salt +X ppm | liters × X ÷ 1,000 |
| Total alkalinity −X ppm, with muriatic acid | liters × X × 36.46 ÷ 50.0 ÷ 1,000 grams of HCl |
The numbers 84.0, 111.0 and 36.46 are the molar masses of baking soda, calcium chloride and hydrogen chloride. Alkalinity and hardness are reported "as calcium carbonate", which is where 50.0 and 100.1 come from.
The product amount is the active grams divided by the strength on the label. Dry products use the percent by weight. Liquid chlorine is sold by "trade percent", grams of available chlorine per 100 mL, so a liquid dose is grams ÷ (percent × 10) × 1,000 mL. Household bleach labels give percent by weight instead, so a bleach result can be off by a few percent. Muriatic acid is taken as 31.45% HCl at 1.16 g/mL.
To lower stabilizer, calcium or salt, chemicals don't help. The calculator gives the share of water to replace instead: 1 − target ÷ current. That assumes your fill water contains none.
Check against published tables
Health departments publish dose tables for 10,000 gallons. The formula above gives the same answers, within their rounding:
| Change in 10,000 gallons | This calculator | Indiana Dept. of Health table |
|---|---|---|
| +1 ppm chlorine, liquid 12% | 10.7 fl oz | 10.7 fl oz |
| +1 ppm chlorine, cal-hypo 67% | 2.0 oz | 2 oz |
| +1 ppm chlorine, trichlor 90% | 1.5 oz | 1.5 oz |
| +1 ppm chlorine, dichlor 56% | 2.4 oz | 2.4 oz |
| +10 ppm alkalinity, baking soda | 1.4 lb | 1.4 lb |
| −10 ppm alkalinity, muriatic acid 31.45% | 25.6 fl oz | 26 fl oz |
| +10 ppm calcium, calcium chloride 100% | 0.93 lb | 0.9 lb |
| +10 ppm cyanuric acid | 13.4 oz | 13 oz |
pH is not in the calculator. How much acid or soda ash moves pH depends on your alkalinity and other water conditions, and published figures are only rough starting points.
Common target levels
The CDC recommends pH 7.0–7.8 and at least 1 ppm free chlorine in pools (3 ppm in hot tubs). If your pool uses cyanuric acid, keep chlorine at 2 ppm or more. The CDC also advises testing chlorine and pH at least twice a day, and says DPD test kits are the most accurate (CDC).
Public pools follow state codes. Columbus Public Health (Ohio), for example, lists ideal ranges of 2–4 ppm free chlorine, pH 7.4–7.6, 80–120 ppm alkalinity, 200–400 ppm calcium hardness and 30–50 ppm cyanuric acid, and closes a pool above 100 ppm cyanuric acid (Columbus Public Health). Those rules are written for public pools, but many home owners use them as a guide.
Sources
- Virginia Department of Health, Pool Chemical Safety.
- U.S. Centers for Disease Control and Prevention, Home Pool and Hot Tub Water Treatment and Testing.
- Columbus Public Health, Water Chemistry Parameters.
- Indiana Department of Health, Adjusting Chemical Levels in a Swimming Pool (dose table used as a cross-check).