How do I lower cyanuric acid (CYA) in my pool?

Drain and refill a portion of your pool water—that’s the only reliable way. CYA doesn’t evaporate or break down naturally, so you must physically remove it. Test your current CYA, decide your target (ideally 30-50 ppm), and drain the percentage needed (e.g., 60% if going from 100 to 40 ppm). Don’t drain concrete or gunite pools completely; stick to a third or half at a time. Stop adding tablets or shock with stabilizer until you fix the CYA.