This is my first post with this group. I had stains appear during the winter. Pool center said high in minerals. As a result of several conversations, we disconnected the ozone system and Nature2 system. Changed the sand. Water is clear but stains won't leave. When I add shock the stains go to a darker gray or black. Won't stub off. Over 24 hours, darkness fades, but stains are still there. I am truly stumped. Am I fighting algae or metals or both? Getting different recommendations from pool centers. We have a leaf problem in the winter, which we skim up. Pool runs all year long. This is the first time we have had this problem in 5 years. Even the return gets have turned a dingy yellowish brown. I hope someone can help me. Thanks