Hi, this was the first year I opened my pool. I hired a company to come out and get it started for me, but I took over getting the pool chemicals balanced. The pool was green and filled with algae. It's been a few weeks since it has been open. The water looks great, except for these stains around the bottom edges of the pool. I've scrubbed them, but haven't been able to get any off. I also tried holding a chlorine puck against it, but that didn't do much either. I have my pool at shock level now, but nothing seems to be getting rid of these stains. Does anyone have any recommendations? Do you think it's mustard algae. It definitely looks organic to me. Here are my most recent test results.
CYA- 30- it was at 0, but I brought it up to 30 recently.
FYI- The pool is plaster.