Quote Originally Posted by mbar
I would follow what Dave said. I think you are dealing with algae, because if you can rub the stain off with a brush, then it isn't a metal stain. I would go ahead and put the metal free in before you add the chlorine, it will bind with any metal that may be in solution, and then I would put a chlorine puck in your skimmer so that if there is staining, it will stain the filter first. You must have your ph down to 7.0, 7.2 for the chlorine to work the best, and the more acidic the pool, the less chance of it staining with high chlorine. I would keep the chlorine at shock levels for at least a week, and especially until the water is holding the chlorine with no combined chlorine. Don't add any cya if you have it at 65, that is high enough. Have some patience - the water won't clear over night, but you will be able to see improvement day to day. Don't worry about the stain coming back - if it does, you will be able to treat it, but for now you have to make sure there is no algae in your pool. You can swim with stains, but you can't swim with algae!!. Put metal free in, bring down your ph, and add lots of bleach - put a puck in the skimmer. keep the filter running 24/7. Keep us posted & best of luck.
Chlorine puck in the skimmer is NOt a good idea with a cartridge filter. The very low pH of trichlor can actually ruin the cartridge (happened to me when my pool was being built. Before they got the SWG working they were puting trichlor pucks in the skimmer and it started to dissolve the rubber (or plastic) ends on the cartridge and put goo from it all inside the filter and into my pool! My builder actually fired one of his guys who did this and ended up having to replace my entire filter which was only about 2 months old at the time)