Quote Originally Posted by apoolman
I am a CPO by the www.nspf.com

I The 3 inches of the top of the surface is where the CYA does its job.
Well, you are right about that, CYA protects the chlorine from degradation by UV rays and they only penetrate abot 3 inches below the surface of the water before they are greatly reduced!. Not much need to protect the chlorine from degredation by UV at the bottom of the pool! Once again, what you stated goes against everything I know about the chemistry of solutions.