Removes black cobalt stains from fiberglass spas and swimming pools. See the fabulous results below.Removes copper and iron stains from plaster swimming pools. An excellent product for removal of metallic stains from spas and pools.Stable at high temperatures and is unaffected by chlorine, acid or other sanitizing chemicals. Mixes very rapidly with pool water. Swimming may begin or continue 30 minutes after treatment. BIO-DEX PRODUCTS ARE GUARANTEED TO WORKWHEN USED AS DIRECTED.