What Is CYA (Cyanuric Acid)?
Cyanuric Acid (CYA) is a chlorine stabilizer used in outdoor pools. Its primary role is to protect free chlorine from degradation by the sun’s ultraviolet (UV) rays. Without CYA, sunlight can destroy the majority of free chlorine within a few hours, reducing sanitization and increasing chemical costs.
How CYA Works
Think of CYA as sunscreen for chlorine. It forms a protective bond with free chlorine molecules, reducing UV-driven decomposition so chlorine remains active in the water longer. This extends the effective life of each chlorine dose and helps maintain consistent sanitization.
Recommended CYA Levels
| Pool Type | Ideal CYA Range (ppm) |
|---|---|
| Outdoor chlorine pools | 30–50 ppm |
| Saltwater pools (with saltwater chlorine generators) | 60–80 ppm |
| Indoor pools | 0–20 ppm (usually not required) |
Note: Too little CYA allows rapid chlorine loss from sunlight. Too much CYA reduces chlorine’s disinfecting power — which can lead to cloudy water, algae, and sanitizer struggles.
Why High CYA Can Be a Problem
Excessively high CYA can cause a phenomenon often called “chlorine lock,” where free chlorine is present but less effective. When CYA rises, you must maintain a higher free chlorine (FC) concentration to achieve the same sanitizing effect.
| CYA Level (ppm) | Typical Minimum FC Suggested |
|---|---|
| 30 ppm | 2–4 ppm |
| 80 ppm | 6–9 ppm |
| 100+ ppm | 10+ ppm (undesirable) |
How CYA Gets Into Your Pool
Primary sources of CYA are stabilized chlorine products (which combine chlorine and cyanuric acid), including:
- Dichlor (sodium dichloro-s-triazinetrione)
- Trichlor tablets (slow-dissolving chlorine tablets)
- Granular or liquid CYA stabilizer products
- Some “stabilized” shock products
How to Raise or Lower CYA
To Raise CYA
Add a cyanuric acid stabilizer product according to the manufacturer’s directions. Always add gradually and retest the water after 24–48 hours.
To Lower CYA
Because CYA does not dissipate quickly, the reliable way to lower it is dilution:
- Partially drain and refill the pool with fresh water.
- Use frequent backwashing (for sand/DE systems) where applicable.
- Consider professional reverse osmosis (RO) services if water replacement is difficult in your area.
Best Practices for Managing CYA
- Test CYA monthly during swim season and after major additions/refills.
- Use non-stabilized liquid chlorine (sodium hypochlorite) or unstabilized granular chlorine if your CYA is trending high.
- Keep a balanced ratio of free chlorine to CYA — follow recommended minimum FC for your CYA level.
- When using stabilized tablets, place them in a floater or feeder away from direct contact with pool surfaces and equipment.
Tip: Many pool test kits measure CYA directly; if yours doesn’t, bring a sample to a professional pool store or use a reliable test kit (D.I.Y. tests and strip tests vary in accuracy).
Final Takeaway
Cyanuric Acid is essential for outdoor pools because it protects chlorine from sunlight and reduces chemical waste. That said, balance is critical — keep CYA within the recommended range and maintain appropriate free chlorine levels so your pool stays clean, clear, and safe.
