Thanks chem geek. Regarding disappearing CYA, I thought that would only happen if you close the pool down and let it turn into a green sludge pond. I've never done that. As I noted in my prior post, mine was circulating all winter and was well chlorinated at all times. Under those conditions, is there any other mechanism that would consume CYA? The recurring yellow algae perhaps?

I'll reduce the FC as you suggested, but at the first sign of the yellow beast, I'm taking it back up again. This is the lowest my CYA has been in a long time, so I want to take advantage of it and rid my pool of this hard-to-kill algae.

Regarding phosphates, did you read what PoolDoc said in post #51 about "attached" phosphates? Do you agree? Should I just keep dosing with Orenda until I see a breakthrough below 300?

Thanks,
Mike