Spring 2012 I used a product called Green Out when opening the pool to help clear out algea. It required a high PH before adding the product so I used PH-Up a couple of pounds at a time till I got to the PH range. My water got very cloudy and when things cleared up I noticed my white pool plaster had various areas that had turned a dirty gray/brown kind of swirled pattern. When I tried to remove it nothing worked, it had fused with the plaster. I noticed when I sprinkled shock around that if the granules hit these areas before dissolving that these areas would turn black for awhile until the shock dissipated. Did not get this resolved in 2012, and this spring and summer the problem persists. It might be being compounded by DE media which seems to be getting past/through the DE filter. When sweeping the pool I stir up clouds of dust that has settled on the pool bottom. It's a 24,000 gallon gunnite/plaster pool that was resurfaced four years ago.
Looking for suggestions,