Can anyone venture a guess as to what these spots may be? I realize the clarity of the picture isn't great, but it was the best that I could do today. They are darkish-brown in color and will not brush up with a regular pool brush. They are both in the shallow end and deep end of the pool. My guess is that they are more prominent in the "blistered" areas of my fiberglass pool. Below is my photobucket link.
http://i1016.photobucket.com/albums/af2 ... ots001.jpg