My angels that I had would frequently pick at algae in my tank. As Gerry said they are voracious eaters and more prone then other fish to overeating.

I am curious if these are recently purchased fish. I have found that angels can be very difficult to acclimate at times. I like to see them alive in my LFS tank for a week or two before I purchase. I have had angels that have acted similarly in the past to yours, but without the bloat.

Do the scales puff out in the stomach area? Is the stomach symmetrical or bloated on one side?

Fred