Water Chemistry
A pool additive that protects chlorine from UV degradation in outdoor pools. Essential in moderation, counterproductive above 70ppm.
Cyanuric acid (sold as `stabilizer` or `conditioner`) shields chlorine from breaking down under direct sunlight. Outdoor pools without CYA lose chlorine rapidly and demand much heavier dosing. The trap: CYA accumulates with every trichlor tablet added, and above 70ppm it can trigger `chlorine lock` — chlorine reads on the test but becomes ineffective at killing bacteria. Illinois IDPH allows up to 100ppm, but most county inspectors flag anything above 50–60ppm. The only way to reduce CYA is to partially drain and refill the pool.
More stabilizer is not better — it caps at a functional ceiling around 50ppm.
CYA does not `burn off` on its own. Dilution is the only reduction method.
`Chlorine lock` does not mean your chlorine is gone. It means it's reading on the test but not sanitizing effectively.
Read more on the blog
Related terms · Water Chemistry
Chlorine Lock
A state in which chlorine test readings appear normal but the chlorine is ineffective at actually sanitizing the pool. Usually caused by excessive cyanuric acid.
Combined Chlorine (Chloramines)
Chlorine that has already reacted with organic contaminants and lost most of its sanitizing value. The primary cause of the strong `chlorine smell` in pools.
Langelier Saturation Index (LSI)
A composite calculation (pH + temperature + calcium hardness + alkalinity + CYA adjustment) that measures whether pool water is corrosive, balanced, or scale-forming.
pH (Pool Water)
A measure of how acidic or basic pool water is on a 0–14 scale. Illinois IDPH requires semi-public pools to hold pH between 7.2 and 7.8, with 7.4–7.6 as the practical operating target.
Aqua-Guard runs certified commercial pool operations for 200+ Chicagoland HOAs, condos, and clubs. We handle the credentials so your board doesn't have to.
Request a Written Proposal