Free chlorine (hypochlorous acid) is highly sensitive to UV light. Without protection, the sun steadily destroys your chlorine throughout the day. In full sun without CYA, you would need to add chlorine multiple times daily just to maintain safe levels.
Cyanuric acid forms a weak, reversible bond with chlorine molecules. This bond blocks UV from degrading the chlorine while keeping the chlorine available to kill pathogens when it comes into contact with them. The result: chlorine lasts hours instead of minutes.
| CYA Level | Effect on Chlorine | Recommendation |
|---|---|---|
| 0 ppm | UV destroys 50% in 17 minutes | Add stabilizer immediately |
| 20–30 ppm | Useful protection, chlorine mostly available | Acceptable minimum |
| 30–50 ppm | Optimal protection and chlorine effectiveness | Target this range |
| 50–80 ppm | Good protection; chlorine slightly less effective | Acceptable; raise chlorine target slightly |
| 80–100 ppm | Chlorine significantly impaired | Consider partial drain |
| Above 100 ppm | Chlorine lock — effectively no sanitation | Drain 50% and refill required |
If you use trichlor tablets as your primary sanitizer, the answer is almost certainly yes — you are already adding CYA with every tablet. Trichlor is about 54% CYA by weight. Each tablet adds roughly 6 ppm of CYA to 10,000 gallons per week.
Always test CYA before adding stabilizer. Over-adding creates chlorine lock that requires a partial drain to fix.
Products that contain CYA:
Products that do NOT add CYA:
Add granular CYA through the skimmer basket with the pump running, or pre-dissolve in a bucket of warm water and pour along the pool edge. Dose: approximately 13 oz of granular CYA per 10,000 gallons raises CYA by 10 ppm.
CYA dissolves slowly — allow 24–48 hours and retest before adding more. Never pre-dissolve CYA in a bucket and add it directly to a pool with bathers present.
CYA does not leave the pool through use, evaporation, or filtration. It only leaves through backwashing and dilution. CYA levels rise throughout the season if you use stabilized chlorine products. Test monthly and plan a partial drain if levels exceed 80 ppm.
SplashLens reminds you when CYA is due for testing and tracks levels over time. Know when CYA is creeping toward chlorine lock — before it becomes a problem.
Open SplashLens Free →Outdoor pools need CYA in the 30–50 ppm range to protect chlorine from UV degradation. Indoor pools do not need stabilizer. If you use trichlor tablets, test CYA first — you may already be at the right level.
Add granular cyanuric acid through the skimmer or pre-dissolve in a bucket. About 13 oz per 10,000 gallons raises CYA by 10 ppm. CYA dissolves slowly — wait 24 hours and retest before adding more.
Yes. CYA above 80–100 ppm causes chlorine lock — your pool cannot be properly sanitized even with adequate free chlorine levels. The only remedy is partial drain and dilution. There is no chemical way to reduce CYA.
They are the same chemical — cyanuric acid. "Pool stabilizer," "pool conditioner," and "chlorine stabilizer" are all marketing names for CYA. The formulation is identical regardless of brand.
Yes — saltwater pools use a chlorine generator that produces unstabilized chlorine. Without CYA, UV degrades it rapidly. Maintain 30–50 ppm CYA in a saltwater pool just as you would in a traditional pool.