A dark stain appeared on my Pebble Tec marcite back in early spring, about 18” long and 12” wide in a fan shape. From above the waterline it appears almost black, but underwater it looks grey/brown (see underwater pics attached).
I first tried rubbing a chlorine tab on it with no results. Later applied muriatic acid via a PVC pipe. The acid temporarily lifted it but it quickly re-deposited in a larger area as the acid drifted toward the deep end. Now it’s about 4’ long. Strangely subsequent treatment with muriatic acid did not affect it. It’s like it has a stronger bond now.
Thinking that it may be iron, I later tried ascorbic acid. Brought pH down to 7.2 and chlorine near zero, put about a half pound in a sock and rubbed it directly on one section of the stain for several minutes, until the AA completely dissolved. No effect. Poured the remaining 1.5 pounds of ascorbic acid in the water over the stain and let it recirculate for a day. Still nothing.
I should add that there are other areas of the pool that appear to have lighter staining than this area, as if there is lighter accumulation of whatever this is. I am not on well water. The pool was constructed 5 years ago.
thanks in advance for any guidance.
I first tried rubbing a chlorine tab on it with no results. Later applied muriatic acid via a PVC pipe. The acid temporarily lifted it but it quickly re-deposited in a larger area as the acid drifted toward the deep end. Now it’s about 4’ long. Strangely subsequent treatment with muriatic acid did not affect it. It’s like it has a stronger bond now.
Thinking that it may be iron, I later tried ascorbic acid. Brought pH down to 7.2 and chlorine near zero, put about a half pound in a sock and rubbed it directly on one section of the stain for several minutes, until the AA completely dissolved. No effect. Poured the remaining 1.5 pounds of ascorbic acid in the water over the stain and let it recirculate for a day. Still nothing.
I should add that there are other areas of the pool that appear to have lighter staining than this area, as if there is lighter accumulation of whatever this is. I am not on well water. The pool was constructed 5 years ago.
thanks in advance for any guidance.
