Is someone able to help me identifying these stains? I just treated with "Stain Free" and also added "Metal Free" with no results. I followed the directions by reducing the chlorine level to 0 and lowered the ph to about 7.2. Brushed the stains and again, no change. Pool is about 23 years old with original plaster. Pool is not screened in. Pool is approximately 10,000 gallons. Stains are primarily in the deep end. They have been present for a couple of years. Any ideas, advice would be greatly appreciated. Btw, I'm located in central florida.