How do I lower high cyanuric acid (CYA) in my pool?

You pretty much have to drain the pool. High CYA is a one-way street — no chemical breaks it down and no filter catches it. Reverse osmosis trucks can remove CYA without draining, but they’re expensive and not always available. Slow dilution via backwashing and refilling works if you’re not in a hurry and CYA isn’t sky-high, but it’s slow and uses a lot of water.