Just recently I had one very distinct brownish stain show up on my wall about 2 feet below the surface in the deep end. It's got a really dark center about the size of a quarter with 3 streaks about 3-6 inches long coming out of it. In the same area there are also a couple small dark blue/black lines. I tried the vitamin c tablet test and it definitely lightened the brownish streaks and made the central stain smaller - after about 15 minutes of rubbing. It did not appear to help the smaller blue/black marks. The next day the entire stain was back though. The only other possible sign of metal in the pool is that my pump strainer basket seems to be turning yellow. There also looks like some bluish streaks at the bottom of the pool under the primary stain.
I've since started to lower my pH which tends to be high (7.8). I've also added some "Metal Control" and ordered some Jack's Magic Pink Stuff and 2lbs of Ascorbic Acid just in case an AA treatment is recommended.
Is it odd to have just one stain that is so distinct? Does free metal in the water tend to deposit in just one place? It is near where an opposing return is directing flow. Is it possible there is metal leeching from the gunnite below the plaster? Perhaps from poorly covered rebar?
Once I get the pH down to 7.2 and get some Magic Jack's Pink in the water, I plan on using dry acid directly on the stain to try to remove it. If that doesn't work, is an AA treatment advised?
Water Temp: 80