You may have caused any metals in your water to fall out and stain the pool surface when you had your chlorine levels high. YOu can tell if the stain is mineral by getting a few vitamin C tablets, crushing them up, putting them in a sock and rubbing on the stain. If the stain lightens or disappears, then it is a mineral (metal) stain. To find out if the stain is organic, you can use a trichlor tablet crushed up and do the same thing. If the stains lightens or disappears, it is organic. To get rid of a metal stain, you can first try to get a sequestering agent, lower the ph down to 7 and use as directed on the bottle. If this doesn't lift the stain, then you can do an ascorbic acid treatment. I can give you the directions for this. If it is an organic stain, then it will go away with high levels of chlorine. Let me know how you do. Don't worry - the stains can be taken care of