You can't safely lower CYA without draining.

No. Every “no-drain” solution is either snake oil or risky.

Cyanuric acid (CYA) is chemically stable. It doesn’t break down naturally, and no pool chemical will remove it. Products that claim to “reduce CYA” are usually just flocculants that clump it so it settles to the bottom, but that’s a band-aid — it can still redissolve, and you’re left vacuuming to waste anyway, which drains water. Same result.

Biological methods (bacteria that eat CYA) exist but are slow, temperature-dependent, and can mess with your chlorine and pH balance. Not worth the headache for most pools.

If you absolutely cannot drain, your best bet is reverse osmosis (RO) filtration. A service truck hooks up and filters out CYA and other dissolved solids without dumping water. It’s not cheap, but it works and doesn’t waste much water. Otherwise, accept that a partial drain and refill is the only reliable, safe fix.

Future You will thank you for just doing the partial drain.