I'm in Gilbert, AZ and have been battling high CYA since I bought this house 2 seasons ago. I just started working on my pool this season and found out my CYA is now around 30, when I started it was over 100. How did you get the CYA reading of 500? If it was from a local pool store, don't put too much value into their test results. Get yourself a Taylor K-2006 kit and test it yourself. As far as high CYA, I just dealt with it and let it lower itself naturally, I had to keep my chlorine levels around 10ppm for the whole season and in the winter I just let the pool filter run but added no chemicals (surprisingly it stays pretty clean, just a little cloudy). I immediately switched to bleach and/or liquid chlorine, this will stop adding CYA too your already high levels as well.