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Why your chlorine target depends on stabilizer
Cyanuric acid (CYA, or stabilizer) shields chlorine from sunlight, which would otherwise destroy most of it within a couple of hours. The trade-off is that CYA also holds on to chlorine, so less of it is free to kill algae and germs. The more stabilizer you have, the higher your free chlorine needs to be to do the same job.
A widely used rule of thumb is to keep free chlorine at at least 7.5% of your CYA (5% for saltwater pools, which generate chlorine continuously), with a comfortable target around 11–12%. With 40 ppm of CYA that means a minimum of 3 ppm and a target near 4.5 ppm. Never let a pool fall below 1 ppm, the CDC minimum for home pools.
Chlorine products compared
| Product | To raise FC 1 ppm in 10,000 gal | Side effects |
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Liquid chlorine loses strength in the heat and over time: a jug that sat in the sun for a month may be well below its label. If your doses fall short, assume a lower percentage.
Safety first: Always read the product label. Add chemicals to water, never water to chemicals. Add one chemical at a time with the pump running, never mix products (especially chlorine and acid), and keep everyone out of the water until levels are back in range. Wear gloves and eye protection when handling acid or shock.
Sources and methodology
Last reviewed: November 2026. Doses are calculated from the chemistry of each product (molecular weights and available chlorine) and cross-checked against manufacturer and industry dosing charts. Recommended ranges follow CDC guidance for home pools and hot tubs.
- CDC – Home pool and hot tub water treatment and testing
- Orenda – Sodium hypochlorite (liquid chlorine) technical notes
Frequently asked questions
How much liquid chlorine raises free chlorine by 1 ppm?
About 10.7 fl oz of 12.5% liquid chlorine raises free chlorine by 1 ppm in 10,000 gallons. With 6% household bleach you need roughly twice as much.
Why does my pool need more chlorine than the bottle says?
Cyanuric acid (stabilizer) protects chlorine from the sun but also slows it down. The more CYA you have, the higher your free chlorine needs to be. A common rule is to keep free chlorine at least 7.5% of your CYA level.
What is the best chlorine for a pool?
Liquid chlorine adds nothing but chlorine and salt, so it is the easiest to balance. Trichlor tablets and dichlor are convenient but add stabilizer every time, and cal-hypo adds calcium. Use the side-effect numbers this calculator shows to keep CYA and calcium under control.
How long after adding chlorine can I swim?
Wait until free chlorine is back in your normal range (usually 1–5 ppm for unstabilized pools) and the product has fully dissolved and circulated, typically 30 minutes to a few hours. After shocking, wait until levels drop.