How much stabilizer to add?
Cyanuric acid is dosed as the pure compound, so the math is direct: about 13 ounces raises 10,000 gallons by 10 ppm. Typical raises:
| Raise CYA by | 10,000 gal | 15,000 gal | 20,000 gal |
|---|---|---|---|
| 10 ppm | 13 oz | 1.3 lb | 1.7 lb |
| 20 ppm | 1.7 lb | 2.5 lb | 3.3 lb |
| 30 ppm | 2.5 lb | 3.8 lb | 5 lb |
Values from the calculator above, which handles any volume and raise.
Granular CYA dissolves slowly and will sit on your floor (or clog a skimmer basket) for days. Put the measured dose in an old sock or stocking, hang it in front of a return jet — or over the ladder — and squeeze it now and then; it'll be gone in a day. Two rules: count the dose as in the water immediately (it is — it's just dissolving), and don't retest for a week, because CYA reads artificially low until it's fully dispersed.
What should CYA be?
| Pool type | CYA range | Why |
|---|---|---|
| Outdoor, chlorine | 30–50 ppm | Enough sun protection without blunting chlorine |
| Outdoor, salt water (SWG) | 60–80 ppm | Cells run efficiently at higher CYA; less chlorine burned off means lower cell output needed |
| Indoor | 0–20 ppm | No sunlight to protect against — CYA only slows the chlorine down |
CYA and chlorine are a matched pair: whatever CYA you settle on sets your FC target. At CYA 40 you're aiming for FC around 4–5; at CYA 70, around 8 for a manually dosed pool. The chlorine calculator has the full table, and this page's result shows the FC target for your chosen CYA. With zero CYA, sunlight destroys half your unstabilized chlorine every couple of hours — an unstabilized outdoor pool is a chlorine subscription you didn't mean to sign up for.
How to lower cyanuric acid in a pool
Water replacement is the only reliable method: CYA doesn't evaporate, doesn't degrade meaningfully in season, and no dose of anything removes it. The math is proportional — to get from 100 ppm to 40 you replace 60% of the water. Enter a target below your current reading above and the calculator gives your exact drain-and-refill percentage; the dilution calculator plans the partial-drain approach in detail (several smaller drains work as well as one big one, and are safer for vinyl liners and high water tables).
As for the "CYA reducer" products: they exist (enzyme/biological treatments), they work slowly when they work, and results across real pools are famously inconsistent. At typical prices, replacing water is usually cheaper and always certain. If someone promises a bottle will fix CYA 150 in a weekend, keep your receipt.
Two possibilities. Below about 20 ppm most test kits simply read "0" — you may just be low. But CYA can also genuinely vanish over winter: under a cover, certain bacteria convert cyanuric acid into ammonia. If that happened, your spring opening will hit a wall of chlorine demand — the ammonia eats FC as fast as you add it. Test, expect to dose heavily until it clears, and then restabilize.
Where high CYA comes from
Almost always from the chlorine itself. Every 10 ppm of FC from trichlor pucks adds about 6 ppm of CYA; from dichlor granules, about 9 ppm. A puck floater running all season quietly adds 30+ ppm of CYA a month — which is how a pool that started spring at 40 ends August at 150, green, and unresponsive to shock. It's not mysterious, it's arithmetic — and it's the main argument for liquid chlorine as your daily driver, with pucks reserved for vacations.