I have an even staining on my pool that turns my blue plaster slightly yellowish. I have had small dark stains that I thought were organic, and put ascorbic acid tablets on them with good success. The immediate area were I have put the tablet had also ridded the area of the yellowish appearance. I think I can really blue up the pool with ascorbic acid.
My concern is I don't know if the yellowish appearance is just organic staining due to age (I have only been in the house for less than a year), or from a metal such as iron. Some people swear if ascorbic acid gets rid of a stain, it has to be iron. Others say they have gotten rid of stubborn organic stains with ascorbic acid. I don't want to use $500 worth of metal sequesterant a year, and there really isn't metal there. You have to add sequesterant on a continual basis. I tested the water for iron and copper at the pool store, and it was zero.
If I do an ascorbic acid treatment, and test the water for metals at that time (after the stains are lifted), could I confirm whether the stains are metals?