Cyanuric acid
Definition
A chemical stabilizer added to outdoor splash pad water to protect free chlorine from UV degradation, kept at 30–50 ppm in most recirculated systems.
Without cyanuric acid (CYA), direct sunlight can destroy 90% of free chlorine in under three hours. CYA bonds with chlorine and releases it gradually, dramatically extending the active disinfection window at outdoor recirculated pads.
Too much CYA — over 100 ppm — locks chlorine up so tightly that it stops killing pathogens, a phenomenon operators call 'chlorine lock.' Most state codes require partial drain-and-refill when CYA exceeds the cap.