I tried to post this before the site went down, but I don't think it went through. Anyway, we recently resurfaced our pool with the Marquis finish & upgraded to a bright blue color, but there are a couple of white stains on the surface of the pool. One is quite large & with the others you can almost see the outline of some footprints the contractors left on the bottom.

Any idea what this is or how we can gently remove them?