Pool stabilizer (CYA) calculator

Stabilizer, or cyanuric acid (CYA), shields chlorine from sunlight. Enter your readings to see how much to add, how much water to replace if it's too high, and the minimum free chlorine for that level.

What level to aim for

• Outdoor pools chlorinated with liquid chlorine, cal-hypo or tablets: about 30–50 ppm is a common target.
• Saltwater pools: often higher, around 60–80 ppm, because the cell produces chlorine steadily and higher CYA protects it through the day. Check your generator's manual, since makers give their own range.
• Indoor pools get little sunlight and often need little or no stabilizer.

More isn't better. Stabilizer holds chlorine in reserve, so the higher the CYA, the more free chlorine you need for the same sanitizing power, and the more chlorine a shock takes. Our chlorine and stabilizer guide explains the relationship.

The formula

One ppm is one milligram per liter, and granular stabilizer is close to pure cyanuric acid. Raising 10,000 gallons (37,854 liters) by 10 ppm takes 378.5 g, about 13.4 oz. Liquid stabilizers are a suspension at a lower strength, so follow their label instead.

Worked example

A newly filled 15,000-gallon outdoor pool has no stabilizer, and you want 40 ppm. 40 × 56,781 ÷ 1,000 ≈ 2,271 g, about 5 lb of granular stabilizer. At 40 ppm, plan to keep free chlorine at about 3 ppm or more.

How to add stabilizer

Granular cyanuric acid dissolves very slowly. Either put it in a mesh bag or an old sock in the skimmer basket and let it dissolve over a few days, or dissolve it in a bucket of warm water and pour it in front of a return jet. Avoid backwashing or cleaning the filter for several days afterward. CYA tests can take up to a week to show the full amount, so wait before adding more.

Too much stabilizer

CYA doesn't evaporate and breaks down only very slowly. The reliable way to lower it is to replace water. Going from 100 ppm to 60 ppm means replacing 40% of the water: (100 − 60) ÷ 100. The drain and refill calculator works it out. Some products claim to break down CYA with enzymes or bacteria. Results vary, so retest carefully if you try one.

The most common cause of high CYA is using trichlor tablets or dichlor all season. Each 1 ppm of chlorine from trichlor adds about 0.6 ppm CYA, and from dichlor about 0.9 ppm. Switching to liquid chlorine for part of the season keeps it in check.

Frequently asked questions

Is stabilizer the same as conditioner or cyanuric acid?

Yes. Stabilizer, conditioner and cyanuric acid (CYA) are the same chemical sold under different names.

How do I test CYA accurately?

The common test is a turbidity test: you add a reagent and see how cloudy the water gets. Do it outdoors in daylight with your back to the sun, and make sure the sample is near room temperature, since cold water reads high. Test strips for CYA are less precise.

Does a saltwater pool need stabilizer?

An outdoor saltwater pool does. Without it, sunlight destroys much of the chlorine the cell produces. Your generator's manual gives a recommended range.