What Is CYA (Cyanuric Acid)?
Cyanuric acid (CYA), also called stabilizer or conditioner, is the chemical that shields free chlorine from sunlight so it lasts. Here is what it means, the right level, and how it shapes your chlorine target.
Cyanuric acid (CYA), commonly called stabilizer or conditioner, is the chemical that protects free chlorine from being destroyed by sunlight, acting like a sunscreen for the chlorine in your pool. Get it right and your chlorine lasts for hours instead of minutes. Get it wrong and you either waste chlorine or struggle to keep the water clear.
CYA in plain English
Sunlight is brutal on unprotected chlorine. On a hot, sunny day an outdoor pool with no stabilizer can lose almost all its free chlorine within a couple of hours. Cyanuric acid solves that. It bonds loosely with free chlorine, holding part of it in reserve and shielding it from UV light. The chlorine is still there, still able to work, just protected.
That protection is why nearly every outdoor pool needs some CYA. The catch is that the same bond that protects chlorine also slows it down, so there is a sweet spot you want to hit, not a more-is-better situation.
The right CYA level
Your target depends on whether you run a chlorine pool or a salt pool.
| Pool type | Ideal CYA | Why |
|---|---|---|
| Chlorine pool | 30 to 50 ppm | Enough sun protection without slowing chlorine too much |
| Salt pool | 60 to 80 ppm | The cell makes chlorine all day, so extra UV protection helps |
| Indoor pool | 0 to 20 ppm | No sunlight, so little or no stabilizer is needed |
Confirm your number with the CYA calculator, which also tells you how much stabilizer to add to reach your target for your pool volume.
Why CYA sets your chlorine target
This is the most important idea in modern pool care: your free chlorine target is tied to your CYA, not a fixed number. The working rule is that free chlorine should sit at roughly 7.5 percent of your CYA. So a pool at 40 ppm CYA wants about 3 ppm FC, while a salt pool at 70 ppm CYA wants closer to 5 ppm.
Ignore this link and you get trouble in both directions. Too little chlorine for your CYA and algae grows even with chlorine in the water. Far too much CYA and you have to run uncomfortably high free chlorine just to keep up. Our full FC/CYA relationship guide walks through the chart, and the chlorine calculator sets your daily dose once you know your CYA.
Signs your CYA is off
- CYA too low: chlorine vanishes within hours, you constantly add more, the pool greens up on hot days.
- CYA too high: chlorine seems present on a test but the water still looks dull or algae appears, and you cannot get ahead without big chlorine doses.
How CYA gets too high
Most owners never add straight stabilizer after opening. CYA still climbs because trichlor tablets and dichlor shock are stabilized, bringing cyanuric acid with every dose. A full season of tablets can push CYA well past 80 ppm without you noticing. If your stabilizer keeps creeping up, your chlorine source is the culprit.
Lowering CYA when it is too high
No product removes cyanuric acid from water. The only dependable fix is dilution: partially drain the pool and refill with fresh water. To cut CYA roughly in half, you replace about half the water. Switching from trichlor tablets to liquid chlorine, which adds no stabilizer, keeps it from climbing again. Our step-by-step how to lower CYA guide covers the drain-and-refill math safely.
The takeaway
Cyanuric acid is the sunscreen that keeps your chlorine alive in sunlight, and it quietly sets your entire chlorine target. Keep it at 30 to 50 ppm for a chlorine pool or 60 to 80 ppm for a salt pool, watch it creep up if you use tablets, and always read your free chlorine against it. Test your own water, set your numbers with the CYA calculator and chlorine calculator, and the rest of pool care gets a lot simpler.
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Frequently Asked Questions
What is a good CYA level for a pool?
For a traditional chlorine pool, aim for 30 to 50 ppm of cyanuric acid. Salt pools run higher, usually 60 to 80 ppm, because the salt cell produces chlorine continuously and benefits from more sun protection. Below 30 ppm your chlorine burns off fast in sunlight. Above the recommended range, chlorine becomes sluggish and you have to run higher free chlorine to compensate.
Is cyanuric acid the same as stabilizer or conditioner?
Yes. Cyanuric acid, CYA, stabilizer, and conditioner all refer to the same chemical. It is sold as a granular acid or built into trichlor and dichlor chlorine products. Whatever the label calls it, its job is identical: to shield free chlorine from sunlight so it lasts longer in the water rather than burning off within hours.
How do I lower CYA if it is too high?
There is no chemical that removes cyanuric acid. The only reliable way to lower CYA is dilution: drain part of the pool and refill with fresh water. If your CYA is 100 ppm and you want 50, you replace roughly half the water. Switching off stabilized chlorine like trichlor tablets stops it from climbing again. See our guide on how to lower CYA.
Why does high CYA make chlorine less effective?
Cyanuric acid binds to free chlorine and holds it in reserve, protected from the sun. That is helpful, but it also slows how aggressively chlorine sanitizes. The more CYA in the water, the more free chlorine you need for the same germ-killing power. Run too little FC for your CYA and you can get algae even though a test shows chlorine present.
Do trichlor tablets raise CYA?
Yes. Trichlor tablets and dichlor shock are stabilized, meaning each addition brings cyanuric acid with it. Over a season of tablet use, CYA creeps up steadily and can climb past the ideal range without you adding stabilizer on purpose. If your CYA keeps rising, your chlorine source is usually the reason, and switching to liquid chlorine stops the climb.
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