Congrats on clearing your pool. When I first opened my pool I figured the pool store was where I would learn everything. After discovering this site and then asking questions at the store about what I read, it became clear that they didn't know everything they should. I've been reading your posts (and others) to keep me aware of problems that CAN happen if I don't stay on top of my pool. I find it very soothing actually to go out and take care of it. Thanks mostly for the pics so I can clearly see what a major algae problem looks like. Your filter DEFINITELY looks like a leak to me. I have a DE filter but I had a puddle just like that under mine when I first started the season. My drain plug in the back was leaking, slowly, but enough to make a puddle. I had to shut the pump off, drain the filter, take the plug off, put some new Teflon tape on the threads and put it back. It stopped the leak, but for some reason I was paranoid and tightened it more only to crack the plug and have it leak again!