Add granular stabilizer
What stabilizer does
Sunlight destroys unprotected chlorine fast: an outdoor pool without stabilizer can lose most of its chlorine in a sunny afternoon. Cyanuric acid (CYA) binds loosely to chlorine and shields it from UV light, so your chlorine lasts days instead of hours.
But CYA also reduces how strongly chlorine acts. That is why the right free chlorine level depends on your CYA: the chlorine calculator sets your target automatically from it.
Recommended CYA levels
| Pool | Typical CYA |
|---|---|
| Outdoor chlorine pool | 30–50 ppm |
| Saltwater pool | 60–80 ppm |
| Indoor pool | 0–20 ppm |
| Hot tub | None (CDC recommends against it) |
Many health departments cap CYA at 100 ppm for public pools; above that, chlorine becomes too weak to sanitize reliably.
How to lower CYA
Cyanuric acid does not break down or evaporate, so the only practical way to lower it is to replace water. To go from 80 to 40 ppm you need to drain and refill half of your pool. If you use trichlor tablets, every tablet adds CYA: switching to liquid chlorine stops the rise.
Safety first: Always read the product label. Add chemicals to water, never water to chemicals. Add one chemical at a time with the pump running, never mix products (especially chlorine and acid), and keep everyone out of the water until levels are back in range. Wear gloves and eye protection when handling acid or shock.
Sources and methodology
Last reviewed: November 2026. Doses are calculated from the chemistry of each product (molecular weights and available chlorine) and cross-checked against manufacturer and industry dosing charts. Recommended ranges follow CDC guidance for home pools and hot tubs.
- CDC – Home pool and hot tub water treatment and testing
- HealthLink BC – Swimming pool and hot tub water quality
Frequently asked questions
How much stabilizer raises CYA by 10 ppm?
About 13.4 oz (by weight) of granular cyanuric acid raises CYA by 10 ppm in 10,000 gallons.
What CYA level should my pool have?
Typically 30–50 ppm for chlorinated outdoor pools and 60–80 ppm for saltwater pools. Indoor pools and hot tubs usually need none.
Why is my CYA so high?
Trichlor tablets and dichlor add stabilizer every time you use them. Over a season CYA keeps rising, and the only way to lower it is to replace water.
How long does stabilizer take to dissolve?
Granular stabilizer dissolves slowly: put it in a sock or skimmer basket and wait about 48 hours before retesting. Don't backwash during that time.