Reverse osmosis works, but it costs.

Reverse osmosis. That’s the only real option for lowering cyanuric acid without draining and refilling. The truck comes, hooks up to your pool, filters the water through membranes that strip out CYA (and other dissolved solids), then sends clean water back. You lose maybe 15–20% of the water in the process, but you don’t have to dump the whole pool.

The enzyme-based CYA reducers you see online? Best case, they lower levels by 20–30 ppm over a week, and that’s if you follow the instructions perfectly. Worst case, they do nothing. The chemistry is dubious and the results are inconsistent.

So if your CYA is over 100 and you can’t drain (concrete shell, high water table, city restrictions), reverse osmosis is the move. Downside is cost — $400–600 depending on pool size and your location. But that’s cheaper than replacing all the water and rebalancing.

One caveat: if your CYA is only moderately high (60–80), just stop using stabilized chlorine and let splash-out and rain dilute it over time. No need for extreme measures.