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Pool Chlorine Calculator

A flat "1–3 ppm" is why stabilized pools still go green. Your free-chlorine target scales with your CYA — enter both and we'll give you the right dose.

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How to use it

  1. Test both free chlorine and CYA (stabilizer).
  2. Enter them with your volume.
  3. Add liquid chlorine in the evening so the sun doesn't burn it off before it works; re-test the next morning.

The FC/CYA relationship — the part most calculators skip

Cyanuric acid (stabilizer) protects chlorine from sunlight, but it also holds chlorine back — the more CYA you have, the more free chlorine you need to get the same sanitizing power. That's why a single "1–3 ppm" rule fails: 3 ppm at 80 ppm CYA is effectively weak, while the same 3 ppm at 30 ppm CYA is strong. We target about 7.5% of your CYA as free chlorine.

Frequently asked questions

How much chlorine should I add to my pool?
Enough to reach about 7.5% of your CYA as free chlorine. For CYA 40, that's ~3 ppm. The dose depends on how far below target you are and your volume — enter both above.
Why does my pool go green even with chlorine?
Almost always because free chlorine is too low for your CYA. If CYA is 70–80 but you're holding only 2–3 ppm, that's algae-permissive. Raise FC to the CYA-scaled target.
What's the ideal free chlorine level?
There's no single number — it depends on your CYA. Use roughly 7.5% of CYA as the target and never let it fall below ~5%.

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Built & reviewed by a working pool-service pro. Target ranges follow CDC MAHC, PHTA, and Taylor guidance. Doses are starting estimates — add a little less than the max, re-test, and confirm against your product label. Educational tool, not a substitute for a water test or professional advice.