The right chlorine level is a percentage of your CYA, not a fixed number: minimum 7.5%, target 10%. This calculator does that math and converts the gap into an exact dose.
Target 4.0 ppm — raise by 3.0 ppm
At 40 ppm CYA your free-chlorine band is 3.0-6.0 ppm (min-max), ideal 4.0 ppm. SLAM level: 16 ppm.
You are below the 3.0 ppm minimum for your CYA — algae risk territory. Dose today.
Liquid chlorine 10%
57.6 fl oz (7.2 cups)
Cal-hypo 65%
9 oz
Also raises calcium slightly.
Dichlor 56%
10.8 oz
Adds ~0.9 ppm CYA per 1 ppm FC — avoid if CYA is already high.
This calculator gives you today's number. The app remembers your pool.
Chlorine is one number in a system — pH, alkalinity, and CYA all interact. Poolably saves your pool's volume and history, builds the full treatment plan in the right order, and reminds you when to retest — free on iPhone.
Get Poolably freeStabilizer binds most of your chlorine in reserve; only the unbound fraction sanitizes. More CYA means more total chlorine needed for the same killing power — the full mechanism is in the CYA-chlorine relationship. If you do not know your volume, run the volume calculator first; if your CYA is high, the CYA calculator explains your options. Green water already? Start with the green pool fix instead — that is a SLAM job, not a maintenance dose.