Pool Stabilizer (CYA) Calculator

What Is Cyanuric Acid (CYA)?

Cyanuric acid — sold as pool stabilizer or conditioner, and abbreviated CYA — is sunscreen for your chlorine. In direct sun, unprotected free chlorine can be gone in a couple of hours. CYA bonds loosely to chlorine, shields it from UV, and releases it slowly so it's still there at 4 PM doing its job.

Two things make CYA unlike every other chemical you add:

• It doesn't get used up. Chlorine, acid, and baking soda all react and disappear. CYA just sits in the water. The only way it leaves is with the water — splash-out, backwashing, rain overflow, or a drain.
• Nothing removes it. There's no chemical that breaks CYA down in a pool. Too little is a quick fix; too much is a water bill.

That's why this calculator treats the two directions so differently. Raising CYA is a measured dose of stabilizer. Lowering it is a water change, and the calculator tells you how big.

How to Test CYA

The CYA test is the least precise one in your kit. It's a turbidity test: you mix pool water with a reagent, pour it into a tube with a black dot at the bottom, and note the level where the dot disappears. Half art, half science. Do it twice — in the shade, at the same temperature — before you dose from it.

• Liquid drop kits — the Taylor K-2005 (or the K-2006 Salt for salt pools) reads CYA in 10 ppm steps. This is what the calculator expects.
• Test strips — fine for a mid-week gut check, but the CYA pad is the least reliable one on the strip. Don't dose from a strip.
• Smart monitors — an ICO doesn't measure CYA directly, but its ORP graph shows you the effect: sanitizing power nose-diving every afternoon means the chlorine has no protection.

Why CYA Changes How Much Chlorine You Need

The protection isn't free. The more CYA in the water, the more free chlorine you need for the same killing power. The rule of thumb is a minimum free chlorine of 7.5% of your CYA, with about 10% as an everyday target. The calculator prints this for you with every result.

Look at the bottom row. At 120 ppm CYA you'd need 9 ppm of free chlorine just to stay sanitary — which is why a pool with high stabilizer grows algae at "3 ppm chlorine." The chlorine reading is fine; the chlorine just can't work. That's the whole story behind chlorine lock.

Ideal CYA Level by Chlorination Method

There's no single right CYA number. The right target depends on how chlorine gets into your pool, because that decides how fast it's being made and how much sun it has to survive.

Pick your method in the calculator's "How you chlorinate" menu and it sets the target for you. You can still type in your own.

Salt pools are the ones I see running low most often, and they pay for it twice: the cell works harder and chlorine still crashes by mid-afternoon. In my experience, a salt pool held at 70 ppm gets roughly twice the cell life of one running at 20–30. See the full saltwater pool maintenance guide for the rest of the routine.

How to Raise CYA

Low CYA is the easy direction, and the math is simple: 13 oz of pure cyanuric acid raises 10,000 gallons by about 10 ppm. Scale that by your volume and by how far you need to go, and that's your dose. The calculator does the scaling and also corrects for product strength, because not every jug is 100% CYA.

The Sock Method, Step by Step

Granular stabilizer dissolves slowly and it's acidic. Dumped in the skimmer it can sit in your plumbing for days; broadcast on a vinyl liner it bleaches it. The sock method fixes both.

1. Test twice and confirm your gallons. If you're guessing at volume, use the pool volume calculator first. Being 3,000 gallons off changes the dose by 20%.
2. Measure the dose the calculator gives you — and if it's more than one 10 ppm step, weigh out just the first step.
3. Fill an old sock or a leg of pantyhose with the granules and tie it off.
4. Hang it in front of a return jet or set it in the skimmer basket with the pump running. Moving water does the dissolving.
5. Squeeze it every few hours (gloves on) to break up clumps.
6. Wait 48 hours and retest. In cold spring water, give it a week. Add the next step only after the test confirms the first one.

Why 10 ppm at a Time

Because you can't take it back. The most common CYA disaster I see goes like this: add stabilizer Monday, test Wednesday, see almost no change because it hasn't dissolved yet, add more. By the weekend the first dose finally registers and the pool is sitting at 110 ppm with a partial drain in its future. Dose in steps, wait, retest.

Liquid vs. Granular Stabilizer

The calculator handles both. Here's when each one makes sense.

My default is granular. It's cheap, one jug lasts a season, and the sock method makes it painless. I keep liquid for the situation where the pool just got filled, it's 95°F out, and I don't want to lose a week of chlorine while dry stabilizer dissolves. Whichever you pick, switch the "Stabilizer product" menu in the calculator so the dose comes out in the right units.

CYA Dosing Charts

Quick reference for common pool sizes. The calculator gives you the exact number for your volume and your product strength, split into 10 ppm steps.

Granular Cyanuric Acid (100%) Needed to Raise CYA

A 7 lb jug is 112 oz. For a 96% product, add about 4% to these numbers.

Liquid Stabilizer at the Common Label Rate (1 qt per 10,000 gal per 10 ppm)

Liquid strengths vary. Check your bottle's rate and type it into the calculator.

How Much CYA Your Tablets Add

If you sanitize with trichlor, this table is why your stabilizer climbs all summer. A 3-inch tab weighs about 8 oz.

A pool that opened the season at 40 ppm and ran a floater all summer closes it near 100. That's the case for getting off tablets as your primary sanitizer.

How to Lower CYA

There is exactly one reliable way to lower cyanuric acid: replace some of the water. Fresh fill water has zero CYA, so the math is a straight ratio — the share of water you replace is the share of CYA you remove. Enter a target below your current reading and the calculator gives you the percentage, the gallons, and a stage-by-stage plan.

Drain in Stages

Never take a pool down past a third or so in one go. Vinyl liners float and wrinkle, fiberglass shells can lift out of the ground, and even gunite can crack if the water table is high. Instead:

1. Drain about a third, refill, and run the pump for 24 hours.
2. Retest. Each pass removes a third of what's left, so 120 ppm goes 80 → 53 → 36.
3. Repeat until you're in range, then rebalance everything — calcium, alkalinity, and salt all diluted along with the CYA.

The No-Drain Options

• Reverse osmosis (RO) trailers. A mobile RO service filters your pool water in place, stripping CYA (and calcium) without dumping water. Not cheap, not everywhere, but the right call where water is expensive or restricted.
• "CYA reducer" products. These use bacteria or enzymes to slowly digest cyanuric acid. In my experience they're slow, expensive, and inconsistent. I don't count on them.

Stop It From Coming Back

Lowering CYA is wasted effort if the source is still running. Trichlor tabs and dichlor shock both add stabilizer with every dose; liquid chlorine and cal-hypo add none. Once you're back in range, sanitize with unstabilized chlorine and add CYA on purpose, in measured doses, only when a test says you need it. Until you can dilute, run your free chlorine at 7.5–10% of your current CYA so the water stays sanitary in the meantime.

Common CYA Mistakes

• Dumping the whole bag in the skimmer. It dissolves over days, sits in your plumbing, and shows up all at once — usually after you've added a second dose.
• Re-dosing before it registers. The two-day test that "shows nothing" is normal. The one-week test is the truth.
• Dosing from a strip. The CYA pad on a test strip is a rough guess. A drop kit reads to 10 ppm.
• Running a salt pool at 30 ppm. The cell runs flat out, chlorine still crashes every afternoon, and you replace a $500 cell years early.
• Chasing chlorine when CYA is 150. More shock doesn't fix a stabilizer problem. Test CYA whenever "chlorine stops working."
• Forgetting that tabs are stabilizer. If you floated tabs all summer, test CYA before you add a single ounce of conditioner.
• Ignoring the alkalinity effect. Your total alkalinity test counts part of your CYA (about a third of it). At 70 ppm CYA, a TA reading of 100 is closer to 77 ppm of carbonate alkalinity — which matters when you run the LSI calculator.

Pool Stabilizer FAQ

How much cyanuric acid do I add to raise CYA by 10 ppm?

About 13 oz of pure cyanuric acid per 10,000 gallons. A 20,000-gallon pool needs 26 oz (1.6 lbs) per 10 ppm. If your product is less than 100% CYA, divide by the strength — 13 oz of a 96% product raises the same pool about 9.6 ppm.

What should my pool's CYA level be?

30–50 ppm for a pool on liquid chlorine, cal-hypo, or tablets (40 is ideal), 60–80 ppm for a saltwater chlorine generator, and 0–20 ppm for an indoor pool. The calculator sets the target for your chlorination method.

How long does stabilizer take to dissolve and show on a test?

Granular cyanuric acid takes about 48 hours in warm water and up to a week in cold spring water. Liquid stabilizer registers the same day. Don't add a second dose until the first one shows up.

Can I add stabilizer and chlorine at the same time?

Yes, as long as they go in separately — stabilizer in a sock at one return, liquid chlorine poured in front of another, never mixed in the same bucket. If both are low, add the chlorine now to keep the water sanitary, start the stabilizer the same day, and retest both in 48 hours.

Do chlorine tablets raise CYA?

Yes. Trichlor tablets are roughly half cyanuric acid by weight and add about 6 ppm of CYA per pound per 10,000 gallons. Dichlor granules add about the same per pound. Liquid chlorine and cal-hypo add none.

How do I lower cyanuric acid without draining?

A mobile reverse-osmosis service can strip CYA in place, and enzyme-based "CYA reducers" exist but work slowly and unreliably. For most pools, a partial drain and refill in stages is the only dependable fix.

Is liquid stabilizer better than granular?

Liquid is faster — it registers the same day — but usually costs three to four times as much per ppm. Granular is the better everyday choice; liquid earns its price when you need protection today, like a fresh fill in July.

Does CYA affect pH or alkalinity?

Cyanuric acid is a weak acid, so a large dose nudges pH and alkalinity down slightly. It also shows up in your total alkalinity test: roughly a third of your CYA reading is counted as alkalinity, which is why our LSI calculator asks for CYA.

Stabilizer is the quiet parameter that decides whether the chlorine you pay for actually works. Test it monthly, dose it in 10 ppm steps, and keep it matched to how you chlorinate. For the chlorine dose that goes with your new CYA level, use the pool chlorine calculator; for the full balancing order across every parameter, the pool chemistry calculator walks through it; and the weekly pool maintenance guide covers the routine that keeps it all stable.