What Is Cyanuric Acid (Stabilizer) and Why Does It Matter?
Cyanuric acid (CYA) is a stabilizer that protects chlorine in outdoor pools from rapid breakdown by UV sunlight. The ideal level is 30–50 ppm. Too little CYA accelerates chlorine loss, while too much (above 100 ppm) suppresses chlorine's disinfecting power — a condition known as chlorine lock.
Is CYA Needed in Indoor Pools?
No. Indoor pools that are not exposed to UV light do not need a stabilizer — in fact, unnecessary CYA buildup reduces chlorine effectiveness. Stabilizer should only be used in outdoor pools and semi-covered pools exposed to sunlight.
What to Do When CYA Levels Get Too High
There is no chemical way to lower CYA — the only solution is partially draining and diluting the pool with fresh water. For this reason, stabilized chlorine products (such as trichlor tablets) should be dosed carefully over the long term, switching to unstabilized chlorine (liquid chlorine, calcium hypochlorite) when needed.