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

You can’t fix high CYA without draining some water. Cyanuric acid doesn’t evaporate or break down — it only leaves when you physically remove water. The standard fix is a partial drain and refill. Reverse osmosis filtration trucks can also filter it out, but that’s more expensive and not always available. Don’t buy “CYA reducer” bottles — they don’t work and can mess up your chemistry.