Black Stains on my Gunite!
We bought this house in a short sale. The gunite pool had been uncovered for at least two years, if not three. When we saw the pool a year ago, it was practically empty, but looked white (apart from the standingool of black water). Fast forward through a summer, fall, winter and now spring. We decided to drain the pool early because the black water was attracting Mosquitos. On draining, we found a foot and a half of leaves. Once they were removed and the pool power washed, this is what was left, a black bottom. The pool is thirty years old, so we're afraid to acid wash it because we're about a minute away from concrete. Any idea what this is? Black algae? Tannins? Metal (we're have very high iron in the water here). HELP!