Does Your Pool Need More Stabilizer?

Cyanuric acid helps chlorine last in sunlight, but it also changes how much free chlorine you need. Keep testing FC and set the target from measured CYA. Trichlor and dichlor add stabilizer too, so count those additions when deciding whether your pool needs more.

For an outdoor pool dosed manually with chlorine, the guide range here is 30–50 ppm. Use your exact salt-cell manual for a generator’s target. The tool allows additions toward targets up to and including 80 ppm as a management limit. Indoor pools generally don’t need protection from sunlight.

Chlorine keeps working, with a higher FC requirement as CYA rises. The 80 ppm limit is this tool’s ceiling for stabilizer additions. Above it, stop adding stabilizer, review your measured CYA and FC requirements, and use your system manual to plan the next step. Get a safe water-exchange plan for your pool before reducing the water level.

Replacement water with less CYA dilutes it. In an ideal exchange with zero-CYA water, replacing two thirds of the original water brings 120 ppm down to 40 ppm. You’ll need more replacement water if it mixes during the exchange. Before lowering the level, have a qualified professional assess construction, liner support and groundwater and plan the exchange.

Wait at least seven days after the first addition, or longer if your label or test instructions require. Test CYA again and calculate a new dose; never add the original remainder automatically. Include any stabilizer added by trichlor or dichlor while you waited.