Partial drain is the only fix for high CYA.

You have to drain some water. There is no chemical that lowers cyanuric acid. No magic additive. No filter media. Only dilution.

CYA builds up when you use stabilized chlorine (dichlor, trichlor pucks). It doesn’t evaporate or get filtered out. Once it’s over 100 ppm (or really over 70–80), your chlorine stops working well because it’s “locked up.” You can add more chlorine to compensate, but that’s a band-aid that gets expensive and doesn’t fix the root problem.

The fix: drain a portion of your pool and refill with fresh water. How much? It depends on your target. If you’re at 150 ppm and want to get to 50 ppm, you need to replace about two-thirds of the water (1 - 50/150 = 0.67). Test first, do the math, and drain accordingly. A submersible pump speeds this up.

Future tip: stop using pucks as your primary chlorine source. Switch to liquid chlorine or a salt system. Use pucks only occasionally. Your CYA will stay in check.

If you’re in a drought area or have water restrictions, check local rules before draining. Some places allow partial drain with notification. Better to know before you empty half the pool.