We had a fiberglass pools installed. Work is still undergoing around the pool. Anyway, after backfilling and filling the pool with water, a concrete collar was poured around the pool, although the actual patio around it will be pavers. This was done, I was told, mainly to keep the stairs and seating areas from sagging and partly to accomodate an on-deck automatic pool cover (keep the cover tracks from sagging with the pavers).

We just had the pool cleaned and have noticed thousands of rusty brown spots all over the steps, the seats and basically all around the edge of the pool. These appears to be consistent with splatter from pouring the concrete. There are also a lot bits of concrete on the edge of the pool that is above the water line, but these can easily be removed with the finger nail.

However, the rusty brown spots that are present on the surface of the pool underwater do not come off with either the finger nail or a stiff plastic brush. It has been raining for the past few days and the contractor has not been back on site so we didn't get a chance to ask him about this. I just wanted to get the opinion of the members here as to what they are so I can have an informed discussion with the contractor when he comes back. Thank you in advance.