Partial drain is the only real fix for high CYA.

You can’t — not really. Cyanuric acid doesn’t break down on its own, and no chemical additive will lower it. The only practical way to reduce it without a full drain is a partial drain and refill.

That’s it. Drain 30–50% of the pool, refill, test again. Repeat if necessary. CYA is measured in parts per million, so every gallon you remove takes some with it. You don’t need to drain the whole thing unless levels are truly insane (200+ ppm). A partial drain usually gets you back to the 30–50 ppm sweet spot.

There are two alternatives worth mentioning, but I wouldn’t count on them:

• Reverse osmosis filtration – a truck comes and filters the water, removing CYA. Effective, but costs $400–$800 depending on pool size. Worth it if you have a water shortage or just hate draining.
• Bio-based CYA reducers – products like Bio-Active or “CYA Reducer” use bacteria that eat CYA. They work, but slowly (weeks), and require constant monitoring and aeration. Fine if you’re patient, but not a quick fix.

Bottom line: If you want a fast, reliable solution, grab a sump pump and start draining. A few hours of work now beats fighting algae all summer.