Let me start out by saying thank you to the forum for all the valuable information. Last summer I couldn't control the algae no matter how high my chlorine was, and my pool store did nothing to help me other than sell me more and more chemicals. Little did I know there was something called CYA that I had been pumping into my pool with all those chemicals they were selling me that made my chlorine all but useless. (even at 15 ppm). I estimate that my CYA had been well over 300 because I replaced 75% of my water and my CYA was still over 100. I just replaced 40% of it again this weekend and am now down to 60.
I also want to thank you guys for all the information on chlorine injection. I installed a Stenner chlorine pump and tank this weekend. I got the pump and tank on sale from US Water Systems on Good Friday ($325 delivered ). I just now got around to installing it since the pool was out of service for the winter.
On an unrelated subject, is it normal to get cracks in the plaster? We have a sitting bench in our deep end and there's a hairline crack running diagonally out from the corner of that seating area down the wall of the pool. The crack is about twelve inches long. Our pool is 7 years old. Should this be a concern to me?