Compare draining, managing higher chlorine targets, and changing chlorine products.
Cyanuric acid, commonly called CYA or stabilizer, protects chlorine from being destroyed too quickly by sunlight. That protection is useful, but too much CYA can make routine chlorine management harder because a higher Free Chlorine level is needed to maintain the same sanitizing strength.
CYA usually rises from repeated use of stabilized chlorine products such as trichlor tablets and dichlor shock. Because CYA does not evaporate with pool water, it can build up over time unless water is physically removed and replaced.
Draining may not be safe for every pool. Vinyl liners can shift or wrinkle, fiberglass shells can move, and high groundwater can create pressure beneath the pool. Local discharge rules may also restrict where pool water can be released.
Once CYA is back in a manageable range, use stabilized chlorine only when the pool actually needs additional stabilizer. Regular testing helps prevent the level from quietly climbing again.