I had a Diamond Brite surface applied to my pool about 4 years ago. Within the last 4 months it has developed raised, rough, dark gray and some white blemishes. They range in size from a dime to a 50 cent piece. In my 25 x 12 foot pool there are now about 30 of these blemishes. More seem to develop all the time.
I use a pool service and I was concerned that perhaps a chemical imbalance was causing it. They claim that this is due to improper application of the Diamond Brite. They said that sometimes installers will mix calcium with the Diamond Brite to make it set up more quickly and make it easier to work with and that these spots are due to the that. They said that it takes 4 to 5 years for the calcium problems to occur.
They suggested that a pumice stone could be used to remove the calcium spots but I had to be careful not to take a chunk out of the surface.