Quote Originally Posted by waterbear
From your description this could be cobalt....only seems to happen to fiberglass pools from what I understand.
I believe you are right. It seems to be the only alternative left. I did some poking around on the web and found two products that deal with Cobalt staining; "Cobalt Cure" (United Chemical) and "Jack's Magic". The United Chemical has a better feel to it so I guess I will give it a try. The process is very similair to the advice in the "Brown stains spreading" thread. I wonder what the main ingredient is in Cobalt Cure?

Best,

Steve