Was just doing a quick search on the internet and stumbled on to this forum. Looks like a great resource!! Anyway, we just had about 15 or 20 new stains appear this summer on the bottom of our 3 year old plaster pool. They are ring shaped, which are oblong (not round). Sort of like a skinney "0", if that makes any sense. I am concerned that this might be rebar bleeding through the plaster, but I sure don't remember seeing any rebar sticking through the gunite when the pool was being constructed. Is this a common problem? Does anyone no what it looks like if it occurs? I have tried a stain removal chemical which I bought from the pool store, but unfortunately can't remember the name of it. I do remember it came with a pretty strong warning about using it with colored plaster. Anyway, it had no affect. One other remote possibility I am thinking is for awhile, there was about an 18" long piece of wire sitting on the bottom with the insulation stripped off on both ends. Not sure how it got in there, probably the dog, but we did not notice it for awhile. I'm wondering if that could have caused the stains as well, which I would be a much better problem I think than rebar stains, but I think that might be wishful thinking on my part. Any advise on this would be great appreciated. Thanks!