Partial drain and refill is the only reliable fix.

That’s it. Cyanuric acid doesn’t evaporate or filter out, so lowering it means removing water that contains it and replacing with fresh.

You can mess around with reverse osmosis trucks or expensive bio treatments, but draining and refilling is faster, cheaper, and actually works. The other options exist for people who can’t drain (well water concerns, strict local codes, fancy fiberglass pools), but for most residential pools, just pull out 1/4 to 1/3 of the water and refill.

Test after you top off to make sure you hit your target. Partial drains are the pool equivalent of changing the oil—boring, but necessary.