How do you get metal stains out of a vinyl swimming pool? Have tried several things, better but not gone.?

Without the lowering of the pH, you are not likely to remove the stains. Some pool stores sell oxalic acid. This can help in removing the stains and can be added to the acidic pool. This material will react will chlorine, so add only when the chlorine level is very low.

Put 1/2 pound of pH reducer powder in a white sock, shut off the filter and drop onto a stained area. Check after 15-30 minutes. If improvement is seen, this would be indicative that chemical treatment might work. Chemical treatment will require that you add 2-3 doses of a quality mineral treatment, to help prevent further discoloration. Raise the water level above all of the discoloration and staining. Add muriatic acid until the pH has dropped to below 6.0. It may take considerable acid, depending upon the starting pH and the total alkalinity.

If you read the top of this page and the rest of this article it might help more too.

http://www.askalanaquestion.com/pool_stain_problem...

I hope this helps! good luck!