High CYA Quick Decision Tool

Understanding High CYA in Swimming Pools

Cyanuric acid, often called CYA or stabilizer, protects chlorine from being destroyed too quickly by sunlight. That protection is useful, but when CYA becomes too high, the pool needs a higher Free Chlorine level to maintain the same sanitizing strength.

How CYA Becomes Too High

CYA usually builds up from repeated use of stabilized chlorine products such as trichlor tablets and dichlor shock. Because CYA does not evaporate with pool water, it can continue rising until water is physically removed and replaced.

What High CYA Can Cause

• Higher daily Free Chlorine targets.
• More chlorine required during a SLAM Process.
• Higher routine sanitation costs.
• Greater difficulty clearing algae or cloudy water.
• Confusion when chlorine appears adequate but sanitation is weak.

Practical Options

Moderately elevated CYA can sometimes be managed by maintaining the correct Free Chlorine level. When CYA is very high, partial water replacement is usually the most predictable solution. Stopping stabilized chlorine also helps prevent the level from continuing to rise.

Why Pool Type Matters

Draining must be handled carefully. Vinyl liners can shift or wrinkle, while fiberglass and plaster pools may be affected by high groundwater or hydrostatic pressure. Smaller staged water replacements are often safer than one large drain.