Cyanuric Acid (Pool Stabilizer): What It Is and How to Lower It
Cyanuric acid protects pool chlorine from the sun — but too much weakens it. Here's what CYA does, the ideal level, and how to lower it.
Updated June 2026
Quick answer
Cyanuric acid (CYA), also called stabilizer or conditioner, shields free chlorine from being destroyed by UV sunlight. Outdoor pools want about 30–50 ppm. Too little and chlorine burns off in hours; too much and chlorine goes sluggish — and the only real way to lower CYA is to dilute with a partial drain and refresh.
What cyanuric acid does
Sunlight destroys unprotected chlorine fast — an outdoor pool with no stabilizer can lose most of its free chlorine in a few hours. CYA acts like sunscreen for chlorine, holding it in the water longer. That's why outdoor pools need some; indoor pools generally don't.
The catch is balance: as CYA climbs too high, it also binds chlorine so tightly that the chlorine becomes slow and weak — you can have a normal free-chlorine reading and still struggle to keep the water clear. That's the 'chlorine lock' people describe.
Ideal CYA level — and what raises it
| Pool type | Target CYA |
|---|---|
| Outdoor chlorine pool | 30–50 ppm |
| Saltwater pool | 60–80 ppm (often runs higher) |
| Indoor pool | 0 — no UV to protect against |
Stabilized chlorine products (trichlor tablets, dichlor) add CYA every time you use them, so it tends to creep up over a season.
How to lower cyanuric acid
CYA doesn't break down or burn off on its own, so there's no chemical that simply removes it. The reliable fix is dilution: drain part of the pool and refill with fresh water to bring the concentration down, then re-test. If stabilized tablets drove it up, switching some of your dosing to liquid chlorine (which adds no CYA) keeps it from climbing again.
Aquavail tracks CYA alongside your other readings and flags when it's high enough to be holding your chlorine back — so you treat the real cause instead of just adding more chlorine.
Common questions
What is a good cyanuric acid level for a pool?
About 30–50 ppm for a standard outdoor chlorine pool; saltwater pools often target 60–80 ppm. Indoor pools don't need any, since there's no sunlight to protect against.
How do you lower cyanuric acid in a pool?
By dilution — partially drain and refill with fresh water, then re-test. There's no additive that removes CYA. To keep it from rising again, shift some of your chlorination to liquid chlorine, which doesn't add stabilizer.
What is chlorine lock?
It's the common term for chlorine acting weak despite a normal reading, often blamed on very high cyanuric acid binding the chlorine. The practical fix is to lower CYA by diluting the water rather than dumping in more chlorine.
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