This has been a six+ month issue and could really use some expert help with this one. Pool is 4 years old. Discovered a stain that I believed to be a rebar bleed. Pool store told me to drop a sock of vitamin C pills on spot to see what happens. Spot got larger and much darker. Called my pool builder. He drained pool, cut out plaster and found rusty rebar. He repaired and did an acid wash on pool. Our pool plaster has never been even, so I think he tried to do the acid wash to help with that. We refilled and balanced the pool. Although he fixed the stain, their was a larger stain left from the "sock". Went to pool store and they told me to sink another sock of "lo and slow" in pool to see if their was a reaction. I do not usually use low and slow but use muratic acid. Unfortunately now I not only have the "sock shadow" from the previous issue, but now a 10 foot long streak from the stain to the drain! Upset I went to another pool store--I know--I ordered my test kit today--. She told me to try vitamin c again. I did and where this sock was, the stain is even darker! Not sure what to do other that resurface. Called the people at Jack's magic and they said that I have exposed more aggregate and I needed to sand the surface. They also said I should start adding 2qt. of Purple Stuff and then 16oz. weekly after that to control metals in water.
Ph 8 from pool store. I did add 1/2 gal. of muratic before this last vitamin c "test"