How much cyanuric acid to add to protect your chlorine — or how much water to drain to lower it when it’s too high. Built on standard pool-chemistry dosing.
Pool type
Recommended CYA: 30–50 ppm for chlorine / tablet pools.
Nearly pure cyanuric acid and the cheapest option. Slow to dissolve (24–48h+) — pre-dissolve or use a sock, run the pump, and wait ~48 hours before retesting.
Add this much granular stabilizer
6.5 lb (≈ 104 oz)
to raise CYA from 0 to 40 ppm in 20,000 gal
1.3 × (vol ÷ 10,000) × ΔCYA ÷ (purity ÷ 100) → 1.3 × (20,000 ÷ 10,000) × 40 ÷ 1.00
1.3 oz of pure cyanuric acid per 10,000 gal raises CYA 1 ppm (DOH/NSPF).
Nearly pure cyanuric acid and the cheapest option. Slow to dissolve (24–48h+) — pre-dissolve or use a sock, run the pump, and wait ~48 hours before retesting.
Add stabilizer gradually and re-test after ~48 hours before adding more — you can always top up, but you can’t easily take it back out.
Cyanuric acid (CYA), also called stabilizer or conditioner, shields chlorine from sunlight. Without it, UV destroys about half your free chlorine in ~17 minutes and most of it within a few hours — so for any outdoor pool, CYA is essential, not optional.
But it’s a balance: too little and chlorine burns off; too much and chlorine turns sluggish (“over-stabilization”). Aim for 30–50 ppm for a chlorine pool. Because CYA only leaves by draining water, it’s far easier to add a little at a time than to fix an overshoot.
Granular cyanuric acid is nearly pure, and about 13 oz raises CYA by 10 ppm in 10,000 gallons (≈1.3 oz per 1 ppm per 10,000 gal). Enter your volume, current CYA, and target, and the calculator scales that exactly. Add it slowly — CYA is hard to remove, so it’s better to under-shoot and top up.
For a traditional chlorine or tablet pool, aim for 30–50 ppm. Saltwater pools run higher, around 60–80 ppm, because salt systems produce chlorine at a lower rate. Indoor pools and hot tubs don’t need CYA at all (no sunlight).
The only reliable way is to dilute it: drain part of the water and refill with fresh. To go from your current level to a target, drain a fraction equal to 1 − (target ÷ current) — for example, 100 ppm down to 40 ppm means draining about 60% and refilling. Use the “Lower CYA” mode to get the exact gallons.
No — despite the marketing, no chemical reliably removes cyanuric acid from pool water. CYA is very stable and only leaves by removing water (dilution) or, in some regions, a reverse-osmosis mobile filtration service. Don’t waste money on “CYA reducer” additives.
Granular CYA dissolves slowly — 24–48 hours, sometimes longer in cool water. Pre-dissolve it or place it in a sock in the skimmer, keep the pump running, and wait about 48 hours before retesting so you don’t accidentally overdose. Liquid stabilizer registers within hours but costs more.
CYA protects chlorine from sunlight, but too much over-stabilizes it: the chlorine is present but sluggish, so it sanitizes slowly. Past roughly 80–100 ppm you have to keep free chlorine very high to compensate. If tablets (trichlor/dichlor) have pushed your CYA up, dilution is the fix.
How many gallons (or liters) your pool holds — any shape, sloped depths, spas included. The number you need before dosing anything.
Open toolHow much liquid chlorine, bleach, or shock to add to hit your target free chlorine.
Open toolHow much salt to add to reach your salt-chlorine generator’s target level.
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