Draining is the only way to lower cyanuric acid.

Add stabilizer to raise it; drain water to lower it. There’s no chemical trick to remove CYA once it’s in the pool.

Cyanuric acid protects chlorine from the sun. Too little (under 30 ppm) and your chlorine burns off in hours. Too much (over 80–100 ppm) and the chlorine is locked up – it’s there but can’t sanitize. Ideal range for a chlorine pool is 30–50 ppm.

You can add CYA easily with a granular stabilizer or liquid conditioner. But to lower it, you have to partially drain and refill. No shortcuts. If your CYA is high, figure out how much water to replace using a pool calculator. Usually a 25% to 50% drain does it, depending on how sky-high you are.

Don’t ignore it. High CYA is the #1 cause of “I added chlorine but it’s still green” problems.