Enter your pool volume, the current free chlorine reading and the level you want to reach to see how much shock or liquid chlorine to add.
How to use the pool shock calculator
- Enter the pool volume in gallons. If you do not know it, work it out with the pool volume calculator.
- Test the water and enter the free chlorine reading.
- Enter the target. Routine shocking is commonly taken to about 10 ppm; to remove combined chlorine, raise free chlorine by ten times the combined chlorine reading.
- Pick the product and check that the strength matches the label on yours.
Formulas
Increase (ppm) = target − current free chlorine Granular: pounds = increase × gallons × 3.785 ÷ (453,592 × available chlorine as a decimal) Liquid: gallons = increase × pool gallons ÷ (strength % × 10,000)
One part per million is one milligram of chlorine per liter of water. A pound is 453,592 mg and a gallon is 3.785 L, which gives the granular formula. Liquid chlorine strength is a trade percentage, and one gallon of 12.5% liquid raises 10,000 gallons by 12.5 ppm.
Worked example: a 15,000 gallon pool from 1 to 10 ppm
- Increase needed: 10 − 1 = 9 ppm.
- With 65% cal-hypo: 9 × 15,000 × 3.785 ÷ (453,592 × 0.65) = 1.73 lb, so open two 1 lb bags and use most of the second.
- With 12.5% liquid chlorine instead: 9 × 15,000 ÷ (12.5 × 10,000) = 1.08 gallons.
Quick reference
| Product | Amount that raises 10,000 gal by 1 ppm |
|---|---|
| Cal-hypo 65% | 2.1 oz by weight |
| Cal-hypo 73% | 1.8 oz by weight |
| Dichlor 56% | 2.4 oz by weight |
| Liquid chlorine 12.5% | 10.2 fl oz |
| Bleach 6% | 21.3 fl oz |
Questions
How much shock do I need for a 10,000 gallon pool?
One pound of 65% cal-hypo raises 10,000 gallons by about 7.8 ppm, so a routine shock is 1 to 2 lb. An algae problem needs considerably more; follow the dosage on the product for that case.
When should I shock the pool?
At dusk or after dark, with the pump running, because sunlight breaks down unstabilized chlorine quickly. Wait until free chlorine falls back to the normal range, usually 1 to 4 ppm, before swimming, and follow the label on your product.
Is this calculator a substitute for the label?
No. It does the arithmetic for raising chlorine by a set amount. Always read the product label for handling, never mix different chlorine products together, and add the chemical to water, not water to the chemical.