Cyanuric Acid (CYA): Stabilizer Explained
CYA binds a portion of your free chlorine into forms that survive sunlight longer—but as CYA rises, you need more total FC to achieve the same sanitizing effect.
Mechanism: protection vs reserve
Outdoor pools face constant UV-driven chlorine loss (see chlorine breakdown in sunlight). CYA forms reversible complexes with hypochlorite species, slowing photolysis. That’s the “stabilizer” benefit. The tradeoff: not all measured chlorine is equally “active” for fast kill at high CYA, which is why industry guidance emphasizes FC relative to CYA, not FC alone.
Trichlor tablets add both chlorine and CYA over time, so CYA can creep up season after season unless you dilute or switch chlorine sources.
Practical implications
- Test CYA regularly; don’t guess from water clarity alone.
- If FC reads “fine” but algae persists or CC stays high, consider CYA context and chlorine lock scenarios.
- Lowering CYA is usually dilution—partial drain/refill where regulations allow.
Calculator links
Pool CYA Calculator, Chlorine Calculator, Volume Calculator (for drain math).
Related guides
Common Questions
What does CYA do in a pool?
Cyanuric acid buffers free chlorine against UV loss so outdoor pools don’t burn off sanitizer in hours—but it also reduces the fraction of chlorine available for fast disinfection at a given test reading.
How do I lower CYA?
CYA doesn’t evaporate; you lower it by dilution (partial drain and refill) or in some cases treatment per professional guidance—avoid unproven shortcuts.
Does indoor water need CYA?
Often little to none—UV exposure is minimal; follow fill water and local guidance.
Related Pool Chemistry Guides
- Typical range: 1–3 ppm chlorine
- Recommended pH: 7.2–7.6
- Test water regularly
WaterBalanceTools provides practical calculators and guides for pool and hot tub water chemistry. These tools are designed to help maintain safe chlorine, pH, and total alkalinity within a healthy water balance.