candy - how are you determining the CYA values? Are you relying on the pool store or testing yourself using a reliable test kit? I never could get consistent results from the pool store.

It would be difficult to distinguish 200 from 400 using the Taylor test. I bet your CYA was even higher than 230 before the water replacement.

I would get a good test kit (Ben's or the Taylor) and test yourself to see where you really are now. Be warned though, the CYA test is a bit subjective. There are some good posts on this forum on how to conduct the test for reliable results. Good luck.

BTW - the guy at the poolstore who said to change your sand is a knucklehead.