Cyanuric Acid (Stabilizer) Calculator
Calculate the stabilizer to raise cyanuric acid (CYA) to your target, or the dilution needed to bring it down. Enter your pool volume and current and target CYA.
Calculator
Add 2.31 lb of stabilizer to raise cyanuric acid from 0 to 30 ppm (dissolves slowly — allow a few days).
Cyanuric acid (CYA), also called stabilizer or conditioner, is chlorine’s sunscreen. Outdoor pools without it lose free chlorine fast in sunlight, so a modest CYA level — often around 30-50 ppm — makes chlorine last far longer. The trade-off is that higher CYA also weakens chlorine’s bite, so your target free chlorine has to rise with it.
You raise CYA by adding stabilizer, which dissolves slowly over a few days. You cannot chemically remove it: the only reliable way to lower CYA is to drain some water and refill with fresh, so this tool switches to a dilution calculation when your target is below the current level.
Formula
To raise CYA, the tool uses the standard stabilizer increment:
stabilizer (lb) = (Δppm ÷ 13) × (gallons ÷ 10,000)
reflecting that about 1 lb of stabilizer raises 10,000 gallons by roughly 13 ppm, with Δppm = target CYA − current CYA. To lower CYA, dilution is the only real option:
drain (gal) = gallons × (1 − target ÷ current)
Draining that fraction and refilling with CYA-free water brings the level down proportionally.
Worked example
Raising a 10,000-gallon pool from 0 to 30 ppm CYA:
- Δppm = 30 − 0 = 30 ppm.
- stabilizer = (30 ÷ 13) × (10,000 ÷ 10,000) = 2.31 × 1 = 2.31 lb.
- Add it via the skimmer sock or feeder; expect it to fully register over a few days.
To go the other way — lowering from 60 ppm to 30 ppm — drain = 10,000 × (1 − 30 ÷ 60) = 5,000 gallons, i.e. replace half the water.
Managing stabilizer over a season
Stabilizer is slow to dissolve, so add it and wait several days before re-testing; do not keep dosing because the number has not moved yet. The most common route to a runaway CYA level is heavy use of stabilized chlorine (dichlor or trichlor tablets), each of which adds CYA every time. If you rely on those, watch CYA over a season and be ready to dilute.
Because higher CYA demands higher free chlorine, keep CYA modest unless you have a reason to raise it (strong sun, long season). When you do adjust it, revisit your chlorine target so sanitation stays effective. There is no chemical that destroys CYA on demand — dilution or a specialty media are the only ways down, which is why the calculator sizes a drain-and-refill.
Because stabilizer only leaves the water through dilution or splash-out, it is worth being deliberate about how it enters. If you like the convenience of tablets, plan on testing CYA every few weeks and diluting when it climbs too high, rather than discovering a runaway level mid-season. Sizing the correction from a current test — up with stabilizer or down with a measured drain — keeps the pool in range without guesswork.
Frequently asked questions
How much stabilizer to raise cyanuric acid?
Roughly 1 lb of stabilizer raises 10,000 gallons by about 13 ppm of cyanuric acid. To reach 30 ppm in a 10,000-gallon pool you need about 2.3 lb. It dissolves slowly, so allow a few days before re-testing.
How do I lower cyanuric acid?
There is no everyday chemical that removes CYA, so you lower it by dilution: drain part of the water and refill with fresh. To cut CYA in half, replace about half the water. The calculator gives the exact gallons for your target.
What CYA level should I keep?
Many outdoor chlorine pools aim for about 30-50 ppm. Remember that higher CYA means you must hold a higher free chlorine level to sanitize effectively, so more is not better. Follow your test kit and product guidance.
Why does my cyanuric acid keep rising?
Almost always because of stabilized chlorine — dichlor granules and trichlor tablets add CYA every time you use them. Over a season that adds up. Switching some dosing to liquid chlorine or cal-hypo stops the climb.
Does high cyanuric acid stop chlorine from working?
It reduces chlorine's effective strength, so at high CYA you need a proportionally higher free chlorine level to sanitize. Very high CYA can make shocking impractical — at that point diluting the water is usually the better move.