Pool chlorine calculator
How much chlorine does your pool need? The answer depends on your stabilizer, so enter CYA and free chlorine and get the dose for whichever product you have.
Chlorine targets at 30 ppm CYA
Add one of these
| Product | Amount | Side effect |
|---|---|---|
| Liquid chlorine 12.5% | 30.7 fl oz | none |
| Liquid chlorine 10% | 1.2 qt (38 fl oz) | none |
| Household bleach 8.25% | 1.36 qt (44 fl oz) | none |
| Household bleach 6% | 1.94 qt (62 fl oz) | none |
| Cal-hypo 73% | 5.5 oz | +1.4 ppm calcium |
| Cal-hypo 65% | 6.2 oz | +1.4 ppm calcium |
| Dichlor 56% | 7.2 oz | +1.8 ppm CYA |
| Trichlor 90% (tabs) | 4.5 oz | +1.2 ppm CYA |
| Lithium hypochlorite 35% | 11.4 oz | none |
For 15,000 gal. Pour liquid chlorine in front of a return jet with the pump on. Pre-dissolve cal-hypo in a bucket of pool water.
Chemical safety: read the product label first and follow it where it differs from this page. Add acid to water, never water to acid. Never mix chlorine products with acid or with each other, not even in a bucket. Add one chemical at a time with the pump running, wait at least 30 minutes (acid and chlorine: until the next test), and retest before topping up.
Why stabilized pools need more chlorine
Cyanuric acid acts like sunscreen: it binds most of your chlorine so sunlight can’t destroy it in an afternoon. The catch is that bound chlorine barely sanitizes. Only the small unbound share does the work, and that share depends on the ratio of chlorine to CYA, not on the chlorine number alone.
Chlorine-to-CYA ratio7.5%
07.5% minimum40% shock
Protected
At 40 ppm CYA the minimum is about 3 ppm and shock level is about 16 ppm. The same 3 ppm that is plenty in an unstabilized pool still works here. That’s why CDC raises its home-pool floor from 1 to 2 ppm when stabilizer is used, and why high CYA can only be fixed by diluting.
FC/CYA chart
Minimum and target free chlorine by stabilizer level, using the widely used 7.5% minimum and 40% shock ratios (CDC floors of 1 ppm and 2 ppm applied).
| CYA | Min FC | Target FC | Shock FC |
|---|---|---|---|
| 0 | 1 | 1 | 10 |
| 20 | 1.5 | 2.3 | 10 |
| 30 | 2.3 | 3.5 | 12 |
| 40 | 3 | 4.6 | 16 |
| 50 | 3.8 | 5.8 | 20 |
| 60 | 4.5 | 6.9 | 24 |
| 70 | 5.3 | 8.1 | 28 |
| 80 | 6 | 9.2 | 32 |
| 90 | 6.8 | 10.4 | 36 |
| 100 | 7.5 | 11.5 | 40 |
Choosing a chlorine product
Liquid chlorine / bleach adds nothing but chlorine and a little salt. It raises pH briefly, then that rise is cancelled as the chlorine is used up.
Trichlor tabs are convenient and acidic, and add stabilizer every day. Great for building CYA early in the season, a problem once CYA is where you want it.
Dichlor dissolves quickly and adds even more stabilizer per ppm. Useful for small pools and hot tubs that need CYA, not for regular shocking.
Cal-hypo adds calcium. Fine for vinyl pools or low-calcium water; watch hardness in plaster pools with hard fill water.
Questions pool owners ask
How much chlorine do I need for my pool?
It depends on your stabilizer (CYA). CDC’s floor is 1 ppm free chlorine, or 2 ppm if you use stabilizer. With stabilizer, a practical minimum is about 7.5% of your CYA: at 40 ppm CYA keep at least 3 ppm FC, and aim a little higher (around 4–5 ppm) so you don’t dip below between tests.
How much liquid chlorine raises free chlorine by 1 ppm?
About 10 fl oz of 12.5% liquid chlorine per 10,000 gallons, or about 13 fl oz of 10%. For 6% household bleach it is about 21 fl oz. Liquid chlorine loses strength in heat and storage, so an old jug does less.
Can I use household bleach in my pool?
Yes, plain unscented bleach is the same chemical as pool liquid chlorine (sodium hypochlorite), just weaker. Avoid scented, “splash-less” or thickened bleach, which contain additives you don’t want in a pool.
What is the difference between free, combined and total chlorine?
Free chlorine is the chlorine still available to sanitize. Combined chlorine (chloramines) is chlorine that has already reacted with sweat and urine and causes the “pool smell”. Total chlorine is the two added together. Keep combined chlorine at or below about 0.5 ppm; CDC notes most health departments cap it at 0.4 ppm for public pools.
Do chlorine tablets raise stabilizer?
Yes. Trichlor tablets add about 0.6 ppm CYA for every 1 ppm of chlorine they release, and dichlor granules add about 0.9 ppm. Over a season that builds up, which is why many owners switch to liquid chlorine once CYA reaches 50 ppm.
When is chlorine too high to swim?
CDC advises not swimming if free chlorine is above 10 ppm, where standard DPD tests can also bleach out and read falsely low. Wait for it to drop back below your normal target.