How much stabilizer do I need to raise CYA?

About 13 oz of granular stabilizer per 10,000 gallons raises cyanuric acid roughly 10 ppm. To go from 10 to 40 ppm in a 20,000-gallon pool is about 78 oz, right around 5 lb. Round down, let it dissolve, and re-test.

What is the ideal CYA level?

30 to 50 ppm on a standard chlorine pool, and 60 to 80 ppm on a pool with a chlorine generator. Too little and chlorine burns off in the sun; above about 100 ppm chlorine becomes sluggish and usually calls for a partial drain.

How do I add cyanuric acid to a pool?

Place granular stabilizer in a sock in the skimmer basket, or broadcast it over the deep end, with the pump running. It dissolves slowly over 24 to 48 hours, so do not backwash or clean the filter for about 48 hours.

How do I lower CYA if I add too much?

There is no chemical that removes cyanuric acid. The only way down is dilution: drain and refill part of the water, or use a reverse-osmosis service. That is why it pays to round the dose down and re-test.

How to Raise CYA (Cyanuric Acid / Stabilizer) in a Pool

Cyanuric acid — CYA, or "stabilizer" — is chlorine's sunscreen. With none in the water, UV burns your free chlorine off in a couple of hours and you can't hold a reading no matter how much you add. Here's the level to aim for, how much stabilizer to add, and how to do it without staining the plaster.

What CYA actually does

CYA bonds loosely to free chlorine and shields it from the sun's UV. Without it, an unstabilized pool in full sun can lose most of its free chlorine in a couple of hours — you're basically pouring chlorine into a bucket with a hole in it. A little stabilizer slows that loss dramatically, so your chlorine lasts through the day and the dose you added actually sticks.

The ideal range

Aim for 30–50 ppm CYA on a standard chlorine pool. If you run a chlorine generator, go higher — about 60–80 ppm — because the cell makes chlorine slowly and steadily and the extra stabilizer protects it through the day. Too little and chlorine burns off fast; too much (roughly over 100 ppm) and chlorine turns sluggish — a "chlorine lock" that usually calls for a partial drain to fix.

The dose: how much stabilizer

The rule the calculator uses: about 13 oz of granular stabilizer per 10,000 gallons raises CYA roughly 10 ppm. So to lift a 20,000-gallon pool from 10 to 40 ppm (a 30-ppm bump) you'd add about 78 oz — right around 5 lb. Enter your own numbers for an exact figure. CYA calculator →

Step by step

Test first. Get a real CYA reading so you know your starting point — it's easy to overshoot a number you're only guessing at.
Measure the dose for your volume and round down. You can always add more next week; you can't take it back out.
Put it in a sock in the skimmer basket — or broadcast it over the deep end — with the pump running. Granular stabilizer is slow to dissolve, and the sock keeps undissolved, acidic grains off a plaster floor where they can etch or stain.
Let it dissolve over 24–48 hours with the pump running. It won't show up on a test right away.
Don't backwash or clean the filter for about 48 hours — undissolved stabilizer sitting in the filter will just get flushed out before it ever counts.
Re-test after a day or two, then top up if you're still short.

Don't overshoot — it's hard to undo

CYA doesn't burn off or evaporate. The only way down is dilution — draining and refilling part of the water (or a reverse-osmosis service). That's exactly why you round the dose down and creep up on the target. If you're already too high, see how to lower CYA →.

A quick safety note

Granular cyanuric acid is mildly acidic and dusty. Add it to the water, never water to it, keep it away from other pool chemicals (never mix chemicals), and don't breathe the dust. Note too that "dichlor" chlorine and stabilized trichlor tabs raise CYA as a side effect, so if you use them your stabilizer may already be climbing on its own. Always confirm the strength and directions on your product label.

Frequently asked questions

How much stabilizer do I need to raise CYA?: About 13 oz of granular stabilizer per 10,000 gallons raises CYA roughly 10 ppm. Going from 10 to 40 ppm in a 20,000-gallon pool is about 78 oz — right around 5 lb. Round down, let it dissolve, and re-test.
What's the ideal CYA level?: 30–50 ppm on a standard chlorine pool, and 60–80 ppm on a pool with a chlorine generator. Too low and chlorine burns off in the sun; over about 100 ppm chlorine turns sluggish.
How do I add cyanuric acid to a pool?: Put granular stabilizer in a sock in the skimmer basket, or broadcast it over the deep end, with the pump running. It dissolves slowly over 24–48 hours — don't backwash or clean the filter for about 48 hours.
How do I lower CYA if I add too much?: There's no chemical that removes it — only dilution. Drain and refill part of the water, or use a reverse-osmosis service. That's why it pays to round the dose down.

How to Raise CYA (Cyanuric Acid / Stabilizer)