Pool CYA (stabilizer) calculator
Raise CYA with the right amount of stabilizer, or learn exactly how much water to replace to bring it down. Pick how you chlorinate and the target sets itself.
Example numbers are filled in so you can see an answer. Type your own over them.
Don't know your gallons? Work it out here →
Exact geometry at 7.48 gal/ft³. Kidney shapes, diving hoppers and salt/turnover figures live in the full Pool Volume Calculator.
Stabilizer to raise CYA
| Raise by | 10,000 gal (37,854 L) | 15,000 gal (56,781 L) | 20,000 gal (75,708 L) | 30,000 gal (113,562 L) |
|---|---|---|---|---|
| 10 ppm | 13.0 oz (369 g) | 1.2 lb (544 g) | 1.6 lb (726 g) | 2.4 lb (1.1 kg) |
| 20 ppm | 1.6 lb (726 g) | 2.4 lb (1.1 kg) | 3.3 lb (1.5 kg) | 4.9 lb (2.2 kg) |
| 30 ppm | 2.4 lb (1.1 kg) | 3.7 lb (1.7 kg) | 4.9 lb (2.2 kg) | 7.3 lb (3.3 kg) |
How much water to replace
| CYA now | To 40 (chlorine pool) | To 70 (salt pool) |
|---|---|---|
| 80 ppm | 50% | 13% |
| 100 ppm | 60% | 30% |
| 120 ppm | 67% | 42% |
| 150 ppm | 73% | 53% |
Why CYA matters
CYA shields chlorine from sunlight; without it, the sun burns most of it off in a couple of hours. The trade-off is that CYA also holds chlorine in reserve, so the more you have, the more free chlorine you need. That is why your chlorine target and your shock level both come from your CYA.
Under a screen enclosure the cage blocks part of the sun, and Trouble Free Pool notes a caged or covered outdoor pool does not need as much CYA as one in full sun. Treat the targets above as full-sun numbers.
High CYA? The full guide: CYA too high. Deep drains in a high water table need care: an in-ground pool can lift out of the ground, so drain in stages or use a reverse-osmosis service.
Dose: 13.0 oz (369 g) per 10 ppm per 10,000 gallons (Trouble Free Pool). Drain: proportional dilution. Targets: the recommended CYA band on our FC/CYA chart (chlorine pool 30–50, salt pool 60–80).
FAQ
How much stabilizer do I add to raise CYA?
About 13.0 oz (369 g) of granular cyanuric acid raises 10,000 gallons 10 ppm. It dissolves slowly: put it in a sock in the skimmer and wait about a week before you retest, or you will overshoot.
What should my CYA be?
For a pool chlorinated with liquid chlorine, cal-hypo or tablets, 30–50 ppm. For a salt pool, 60–80. The salt-cell makers' own manuals (Pentair, CircuPool, Hayward) print 30–50; we run salt pools higher because the cell makes chlorine slowly all day, and the extra stabilizer keeps the sun from burning it off and lets the cell run at a lower setting.
How do I lower CYA in my pool?
Replace water. CYA does not break down or get used up in a normal pool; it only leaves with the water, and the drop is proportional: replacing half the water halves the CYA. The calculator gives the percentage and gallons, and a staged plan for deep drains.
Do CYA reducer products work?
They are unreliable, and Trouble Free Pool does not count on them. Draining and refilling works every time.
Why does my CYA keep going up?
Trichlor tablets and dichlor add CYA with every dose: about 0.6 ppm of CYA for every 1 ppm of chlorine from trichlor. Switching to liquid chlorine (or a salt cell) once CYA is where you want it stops the climb.