What Is CYA? How Too Much Stabilizer Turns a Pool Green

Does your pool keep turning green, even with chlorine added every week? The problem may be CYA. This guide explains what CYA is and how to fix it.

What Is CYA?

CYA stands for cyanuric acid. Most people call it stabilizer. It works like sunscreen for chlorine. Without it, the Texas sun would burn off most of your chlorine in a few hours.

Why Too Much CYA Is a Problem

A little CYA helps. Too much CYA locks up your chlorine, so it cannot kill algae well. The test may show chlorine in the water, but the pool still turns green.

CYA does not go away on its own. It builds up over time, mostly from chlorine tablets and stabilized shock. Each one adds a little more CYA.

What Is a Good CYA Level?

• Chlorine pools: about 30 to 50 ppm.
• Salt water pools: often about 60 to 80 ppm.
• Too high: above about 90 ppm, chlorine starts to struggle.

Signs Your CYA May Be Too High

• The pool turns green or cloudy between visits.
• You add more and more chlorine, but it does not help.
• You use chlorine tablets all year.
• It has been a long time since the pool was partly drained.

How to Lower CYA

1. Test CYA with a good test kit or at a pool store.
2. Drain part of the pool and add fresh water. This is the most common fix.
3. Test again to check the new level.
4. Switch to unstabilized chlorine, like liquid chlorine, for a while so CYA does not climb again.

Be careful: Do not drain a pool all the way without help. In some cases, an empty pool can be damaged. Ask a pro first.

If your pool is already green, see our page on green pool recovery or water chemistry balancing.

Frequently Asked Questions

Can I lower CYA with chemicals?

There are some products that claim to do this, but draining part of the water and refilling is the most reliable way.

Do salt pools need CYA?

Yes. Salt pools make chlorine, and that chlorine still needs protection from the sun.

How often should CYA be tested?

At least once a month. A weekly test is better in summer.

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