How the chlorine dose is worked out
dose = ppm to add × factor per 1 ppm × gallons ÷ 10,000
The factor depends on the product. Raising free chlorine by 1 ppm in 10,000 gallons takes:
| Product | Amount per 1 ppm |
|---|---|
| Liquid chlorine 12.5 % | 10.7 fl oz |
| Bleach 10 % | 13.4 fl oz |
| Bleach 6 % | 22.3 fl oz |
| Cal-hypo 65 % | 2 oz |
| Cal-hypo 73 % | 1.8 oz |
| Dichlor 56 % | 2.4 oz |
| Trichlor 90 % | 1.5 oz |
A 20,000-gallon pool going from 1 to 3 ppm with 12.5 % liquid chlorine needs 2 × 10.7 × 2 = 42.8 fl oz, about a third of a gallon. With 65 % calcium hypochlorite (cal-hypo) a 5 ppm boost in the same pool takes 20 oz. Pour liquid chlorine in front of a return with the pump running, and dissolve cal-hypo in a bucket of pool water first.
Which product to use
Liquid chlorine and bleach add no stabilizer and no calcium, so they suit pools that already have enough CYA; the liquid chlorine calculator goes deeper on strengths. Cal-hypo is a strong granular shock that adds some calcium; see the pool shock calculator for the amount to shock or SLAM. Dichlor and trichlor (tablets, sticks) add stabilizer with every dose: about 0.9 ppm CYA per ppm of free chlorine for dichlor and 0.6 for trichlor, so they are for pools that need CYA, not a pool at 80 ppm.
Dose factors per 10,000 gallons: Trouble Free Pool, Pool School "Pool Math" and the product labels. CYA added per ppm: Trouble Free Pool forum, "How much does Dichlor and Trichlor affect CYA levels?". Read October 18, 2026.
Frequently asked questions
Can I use granular chlorine to shock a pool?
Yes. Calcium hypochlorite (cal-hypo, 65 to 73 %) is the usual granular shock and raises about 8 ppm per pound in 10,000 gallons. Dissolve it in a bucket of pool water first, pour it in at dusk and keep the pump running.
How do I know how much salt my pool needs?
Salt is dosed from the target on your chlorinator, usually 2,700 to 3,400 ppm: pounds = (target − current) × gallons ÷ 120,000. The salt calculator does this and counts the bags. A salt pool still needs a chlorine reading each week.
Can you put too many chlorine tablets in a pool?
Yes. Trichlor tablets add about 0.6 ppm of stabilizer (CYA) for every 1 ppm of chlorine, so the CYA keeps climbing and locks the chlorine up. Past 80 ppm CYA the usual fix is to drain part of the water.
How much chlorine does a 5,000 litre pool need?
5,000 litres is 1,321 gallons. Raising free chlorine by 1 ppm takes 1.4 fl oz (42 mL) of 12.5 % liquid chlorine, and 5 ppm takes 7.1 fl oz (210 mL). Enter 1,321 gallons above for other products.
How much free chlorine should my pool have?
Keep free chlorine at about 7.5 % of your stabilizer (CYA) level or more: 3 ppm at 40 ppm CYA, 4 ppm at 50. Below that algae can grow; the shock calculator gives the higher level for treating a green pool.