Partial drain and refill is the only reliable way to lower CYA.

Yes, it’s a pain, but that’s the answer.

Cyanuric acid (CYA) doesn’t evaporate and doesn’t break down easily. It just accumulates from stabilized chlorine sources like tablets and shock. No chemical additive or magic filter media will remove it in any meaningful amount. You have to physically take the water out.

Calculate how much to replace: measure current CYA, decide your target (30–50 ppm is typical for outdoor pools), and you need to replace about 50–70% of the water if you’re over 100 ppm. Do it in stages over a few days if you’re worried about ground pressure or liner damage. No need to drain the whole thing at once.

Your chlorine will thank you.