How much chlorine for a 20,000 gallon pool?
To raise free chlorine by 2 ppm in a 20,000 gallon pool, add 41 fl oz of 12.5% liquid chlorine, 85 fl oz of 6% household bleach, or 8 oz of 65% cal-hypo. That's a typical daily dose for a pool in full sun.
Rule of thumb: per 10,000 gallons, 1 gallon of 12.5% liquid chlorine raises free chlorine 12.5 ppm, 1 lb of 65% cal-hypo raises it 7.8 ppm, and 1 lb of dichlor raises it 5.6 ppm. Scale by 2 for 20,000 gallons.
Chlorine doses for 20,000 gallons
| Product | +1 ppm | +2 ppm | +3 ppm | +5 ppm |
|---|---|---|---|---|
| Liquid chlorine 12.5% | 20 fl oz | 41 fl oz | 61 fl oz | 102 fl oz |
| Liquid chlorine 10% | 26 fl oz | 51 fl oz | 77 fl oz | 1 gal |
| Household bleach 6% | 43 fl oz | 85 fl oz | 1 gal | 1 gal 85 fl oz |
| Cal-hypo 65% | 4 oz | 8 oz | 12 oz | 1 lb 5 oz |
| Cal-hypo 73% | 4 oz | 7 oz | 11 oz | 1 lb 2 oz |
| Dichlor 56% | 6 oz | 11 oz | 1 lb 1 oz | 1 lb 13 oz |
What level to hold
Keep free chlorine at about 7.5% of your CYA: 3 ppm at CYA 40, 6 ppm at CYA 80, never under 2. Outdoor pools lose 2 to 4 ppm a day to sunlight in summer, which is why the +2 and +3 columns are the ones you'll use most.
Bleach is fine
Plain 6% household bleach is the same chemical as pool liquid chlorine at half strength. Avoid scented or splashless versions, which contain thickeners.
Trichlor tablets
Tablets in a floater or chlorinator dose continuously, roughly 1 ppm a day per 3 inch tablet in 10,000 gallons. They also add CYA and lower pH, so watch both if you rely on them.
Other pool sizes
Chlorine for a 5,000, 8,000, 10,000, 12,000, 15,000, 18,000, 25,000, 30,000 gallon pool. Not a round number? Use the chlorine calculator with your exact volume, or find it with the volume calculator.
Other chemicals for 20,000 gallons
How much shock for a 20,000 gallon pool, How much salt for a 20,000 gallon pool, How much baking soda for a 20,000 gallon pool.