I'm having the same problem as skillset with stains appearing FREQUENTLY in my fiberglass pool. I added AA a couple of weeks ago to get rid of a really bad stain after having to shock my pool. One week ago the stain re-appeared so I added a whole bottle of metal-free which made the stain disappear. Now the stain is back and once again I've added another bottle of metal free and am hoping the stain is gone by tomorrow when we're having 11 boys over for a little league end of year swim party! My problem is, can I add some bleach tonight while waiting for the stain to disappear? My chlorine level is at .5 and I want to raise it before tomorrows swim party! Help!!