Pool RatioHow to use it
- Test free chlorine (FC) and CYA. A FAS-DPD drop test is far more accurate than strips.
- Target FC ≈ 11.5% of CYA (minimum ≈ 7.5%). With CYA 40, aim for about 4.6 ppm.
- Add in the evening with the pump running; sunlight burns chlorine off during the day.
Example: 10,000 gallons, FC 1 ppm, CYA 40, liquid chlorine 10%
- Target FC for CYA 40 = 4.6 ppm
- Raise by 3.5999999999999996 ppm
- 12.8 fl oz per ppm × 3.5999999999999996 = 46 fl oz
About 46 fl oz (5.8 cups) of 10% liquid chlorine.
Every pool test kit has some error, and products vary in strength, so treat any dose as a starting point: add most of it, circulate, retest, then top up. Never mix chemicals together, and add each one separately to the pool.
Frequently asked questions
How much chlorine should be in a pool?
It depends on stabilizer: keep free chlorine at about 7.5–11.5% of your CYA. With CYA 30 that is 2–3.5 ppm; with CYA 50 it is 4–6 ppm; salt pools at CYA 70 need about 5–8 ppm.
Is bleach the same as pool chlorine?
Unscented household bleach is the same chemical (sodium hypochlorite), just weaker, usually 6–8%. Use plain, unscented bleach without additives and adjust the amount for its strength.
Do tablets and granules add anything else?
Yes. Trichlor tablets and dichlor granules add stabilizer (about 0.6 and 0.9 ppm CYA per ppm of chlorine), and cal-hypo adds calcium. Over a season that builds up, which is why the calculator shows it.