Cyanuric Acid (CYA) in Pools: Safe Levels, Hidden Risks, and Proper Testing
Cyanuric acid (CYA), also known as chlorine stabilizer, is commonly used in outdoor swimming pools to protect free chlorine from rapid degradation caused by sunlight.
When maintained at proper levels, CYA improves chlorine efficiency and reduces chemical loss. However, excessive cyanuric acid is one of the most common and misunderstood causes of unsafe pool water.
What Is Cyanuric Acid and Why Is It Used?
Ultraviolet (UV) radiation can destroy unstabilized chlorine within hours. Cyanuric acid binds with chlorine molecules, shielding them from sunlight and extending their lifespan.
Recommended cyanuric acid level for most outdoor pools: 30–50 ppm.
Why High CYA Levels Are a Hidden Risk
Unlike chlorine, cyanuric acid does not evaporate or break down naturally. It accumulates over time—especially when stabilized chlorine products such as trichlor tablets or dichlor shock are used.
- Free chlorine becomes chemically bound
- Sanitizing effectiveness drops significantly
- Water may appear clear but remain unsafe
To understand how this impacts chlorine performance, read: Why 97% of Pool Chlorine Can Be Inactive
Why Accurate CYA Testing Is Essential
Many pool water problems cannot be solved without knowing the true cyanuric acid concentration. Test strips and basic test kits often lack the precision required to detect dangerous CYA buildup.
Professional pool water analysis relies on digital photometric testing such as the:
Pool & Hot Tub Digital Water Tester
Accurate CYA measurement is the foundation of safe, predictable pool water management.
Frequently Asked Questions About Cyanuric Acid (CYA)
What is cyanuric acid in a swimming pool?
Cyanuric acid is a chlorine stabilizer that protects free chlorine from rapid breakdown due to sunlight.
What is the safe cyanuric acid level for pools?
For most outdoor residential pools, the recommended cyanuric acid range is between 30 and 50 ppm.
Why is high cyanuric acid dangerous?
High CYA binds most of the free chlorine, slowing disinfection and allowing bacteria and algae to survive even if the water looks clear.
Can cyanuric acid be reduced without draining the pool?
No. There is no chemical that reliably removes cyanuric acid from pool water. Partial or complete water replacement is the only effective solution.
How can cyanuric acid be tested accurately?
Digital photometric testing provides the most accurate and repeatable measurement of cyanuric acid and free chlorine levels.
