I have an intex 22'X52" above ground pool. Last year our salt water generator went out and the pool got really nasty. We just drained it and are refilling it now. There is a sandy type substance on the walls of the pool liner. We weren't able I get that off. Does anyone know what that is and how to treat it? I read on an old thread somewhere that it could be mustard algea and to treat with bleach and muratic acid before setting the new salt water pump up... But not sure how much to use!! Can anyone help me with this? Thanks so much!