How this calculator works
Parts per million is milligrams per liter, so a dose is the ppm you want to add multiplied by the volume of water. In US units a gallon of water weighs 8.34 pounds, so 1 ppm in a pool is 8.34 millionths of a pound of chlorine per gallon. That is pure available chlorine. A product that is 65% available chlorine needs 100 ÷ 65 times as much as the pure figure, because the rest of its weight is not chlorine. Liquid chlorine is worked out by volume in the same way.
Worked example: to raise a 15,000 gallon pool from 0 to 10 ppm with 65% calcium hypochlorite you need 10 × 15,000 × 8.34 ÷ 1,000,000 = 1.25 lb of pure chlorine, and ÷ 0.65 that is 1.92 lb, or 30.8 oz of shock. Per 1 ppm in 10,000 gallons that is 2.05 oz of cal hypo, 2.38 oz of dichlor, 1.48 oz of trichlor, or 10.2 fl oz of 12.5% liquid chlorine. A 20,000 gallon pool needs 41.1 oz of cal hypo for the same 10 ppm. The same dose of dichlor would leave about 9 ppm of cyanuric acid, and cal hypo adds about 7 ppm of calcium hardness.
For alkalinity, 1.4 lb of baking soda raises 10,000 gallons by 10 ppm, and about 25.6 fl oz of 31.45% muriatic acid lowers it by 10 ppm. For this pool going from 60 to 100 ppm takes 8.41 lb of baking soda, and going from 120 down to 90 takes 115.0 fl oz of acid.
Assumptions and sources
- These are amounts for clean water: sunlight, debris, algae and swimmers use up chlorine (chlorine demand), so you may need more, and the label of your product has the last word. Never mix chlorine products together or with acid, add chemicals to the water (never water to chemicals), and keep swimmers out until your test shows a safe level.
The formula and a worked example are shown above, so you can check any result by hand. Read how we calculate and check our numbers. Results are estimates for planning: supplier products vary, so check the size printed on the label.
Amount to raise free chlorine in 10,000 gallons
By product strength. Scale up or down with the pool size.
| Product | Per 1 ppm | Per 10 ppm |
|---|---|---|
| Calcium hypochlorite (65%) | 2.1 oz | 20.5 oz |
| Dichlor (56%) | 2.4 oz | 23.8 oz |
| Trichlor (90%) | 1.5 oz | 14.8 oz |
| Liquid chlorine (12.5%) | 10.2 fl oz | 102 fl oz |
| Liquid chlorine (10%) | 12.8 fl oz | 128 fl oz |
Tips before you buy
- Test before you dose, and again after the water has circulated for a few hours. A DPD test kit is more accurate than strips.
- Add the dose with the pump running and the pool empty of swimmers. Granules are best dissolved in a bucket of water first, then poured in (add the chemical to the water, never water to the chemical).
- Trichlor tablets and dichlor raise cyanuric acid each time you use them. If the stabilizer builds up, switch to liquid chlorine or cal hypo for a while.
- Never mix chlorine products with each other or with acid. Store them dry, closed and apart.
- Raise alkalinity with baking soda in small steps and retest after the water has mixed. Acid lowers pH as well as alkalinity, so retest pH too.
Tools & materials for this project
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Frequently asked questions
How much shock do I add to a 15,000 gallon pool?
To raise free chlorine by 10 ppm with 65% calcium hypochlorite, 31 oz (1.9 lb). Per 1 ppm in 10,000 gallons the figure is 2.1 oz. Always check the dose on the label of the product you buy.
How much liquid chlorine do I add to raise the pool 1 ppm?
About 10 fl oz of 12.5% liquid chlorine per 1 ppm in 10,000 gallons, or 13 fl oz of 10%.
How much baking soda raises alkalinity?
About 1.4 lb per 10 ppm in 10,000 gallons. Raising a 15,000 gallon pool from 60 to 100 ppm takes about 8.4 lb.
What free chlorine should a pool have?
CDC advises at least 1 ppm in a pool, and at least 2 ppm if the pool uses cyanuric acid, dichlor or trichlor, with pH between 7.0 and 7.8. Public pools follow local rules.
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Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.