Quarter sized oval shaped ringed rust stains on bottom of pool . . .

[smallpooldad]

These stains appear to be the same as ours

They do not go away with any treatment we have tried so far egg. Ascorbic acid method, high chlorine - 40 ppm for 1 week, stain removers, and the oxalic acid method. We never really removed any stains for 9 years, as we had no idea how to do this, until we found this website.

We use to chlorinate with Tri-Chlor tablets and had a Nature 2, we removed the Nature 2 and now chlorinate with liquid chlorine and recently started using Borax. So the pool was way under chlorinated for 9 years based on high CyA. This is why I hardly ever swam in it as I got ear infections. Now at the correct chlorine (6 ppm) for a CyA of 50-55, I never get them and swim daily.

Although the ascorbic acid method did turn the plaster from brown to white it left it with the faint dollar stains you describe, probably there all the time hidden by the brown iron stain. Like you, we believe that they are impregnated into the plaster from years of neglect.

Needless to say they could be caused by some other metal, but what that might be we have no idea.

A week or so ago we added Borax to 70 ppm, for pH control, and this did help lighten them. We also scrubbed the plaster pool with a stainless steel brush and again this helped to remove some but not all (cloudy pool for two days). It did lighten them.

Some years ago, a neighbor of ours had this same problem. They drained the pool and then had a company come out and sand down the pool with an electric orbital sander using 300 then 500 then higher numbers wet/dry sanding paper from 3M (similar to that used on cars). There pool surface is very smooth so presumably they must have used 1000 or higher grit to get there.

If you do try this, very gently run a tiny trickle of water down the side you are working on, make sure the sander is plugged into a ground fault interrupter and wear thick rubber boots used by anglers and electrical workers. In addition long rubber sleeve electrical workers gloves might be a good precaution.

It did do a good job of removing the stains and of course a small layer of surface plaster. Doubt if it is rebar; if it were it should be then occurring throughout the pool.

Hope this helps, would be good to know how it goes if you try it. Like the bottles say, in fine print, try it in a small area first.

Aloha