Alternative to ascorbic acid to remove stains

[waterbear]

From what I know oxalic acid is more toxic than ascorbic acid (if you read the caution statements on the bottle of oxalic acid product that are absent from the ascorbic acid product you will see what I mean) but works in much the same way. It is extremely effective on iron and to the best of my knowledge is the only thing that really works on cobalt staining in fiberglass pools. (Someone please correct me if I am wrong on that!)

[DavidD]

From what I know oxalic acid is more toxic than ascorbic acid (if you read the caution statements on the bottle of oxalic acid product that are absent from the ascorbic acid product you will see what I mean)

Yeah, I noticed that. It did say it was still safe to swim but it definately seems more toxic.

but works in much the same way. It is extremely effective on iron and to the best of my knowledge is the only thing that really works on cobalt staining in fiberglass pools. (Someone please correct me if I am wrong on that!)

Do you have any idea what color cobalt stains would be and what would cause them?

Dave

[waterbear]

cobalt staining looks like greyish or black spots on the fiberglass. Not sure of the cause but some things I have read seem to point to low calcium levels in the water.