Ok. I noticed a few very small spots on the bottom of the deep end of my pool that wouldn't come off. They are very small, probably less than penny size. I use no type of metal based algaecide etc. I couldn't figure out what had caused the problem...until I dove down to within an few inches with swim goggles and noticed a BB stuck to the bottom.
What can I do about the stains? They are too small to notice but I would still like to remove them.