Quote Originally Posted by PoolDoc View Post
You can test with a vitamin C tablet or, better, some Iron Out (laundry section) held in a wet rag against some of the spots. If either of those lighten the spots, it's iron. Thousands of rusty brown spots sound like someone was grinding or cutting something -- maybe rebar for the deck? -- and didn't watch where the filings went. Do NOT let the contractor take a pass on this one; they may not be possible to remove completely.

Ben
Yes, I believe you are right. We had a concrete deck around the pool with steel mesh. This was cut and removed in order to re-set the pool (pool was off-level and was settling over time - different and long story).

While still under (current) construction the contractor lowered the water level to work on the pool light. At that time he applied muriatic acid to the rust spots that were above the (lowered) water line and than sanded with a 600 grit sand paper and was able to remove those spots. He did try to remove the spots that were still under water with just the sand paper but that didn't work. He told me he would try to lower the water level more when he comes to close the pool for the winter (in a month or so) and get at those spots. Does this sound right to you?

I was afraid the sand paper would scratch the finish, however, after inspecting the places where he removed the spots the finish looks intact and smooth still. He told me that this is the same sandpaper that is used to "finish" the fiberglass after a repair.