I just built my first pool last August. Inground, with a plaster (quartz) finish. Everything was going perfect thanks to this site....so perfect in fact that by the time December rolled around and the water temp was around 45 degrees I ignored my pool. Except for the occasional vacuuming. The water looked great so I didn't really test it. Then the weather warmed up and I started paying attention again and I realized that my CH level was about 75. I've read that anything under 100 can start to eat at the finish. Did I screw up my finish? I've also noticed a couple of stains in the deep end? Will they come out now that I'm bringing my chemicals back in line?