I have the same problem. My CYA test is reading off the charts. I diluted it but still over 200. I diluted 4 times and I think I am over 1000 PPM. I am draining the pool. I could not keep Chlorine in the pool. PH kept going low.(below 6.8) The calculator says 95% water exchange? So I hope I am right in draining it. I do have algae that never really clears up. starts to clear and then comes back. I have ordered the TFT kit so I can start testing CC and FC.