So I have been fighting a little bit of some algae in the new tank (new tank blues...) and I saw this thread and felt my tangs were doing a good job overall, but not as good as others. About 10 day's back I added some frags to the tank and algae started growing onto them. The tang's were completely ignoring these frags though.
So yesterday it finally occurred to me, that this frag rack was maybe too high for the tangs. For the tang's to clean the rack, their caudal fin would be at the waterline or out of the water to bite directly down on the algae. So I moved the frag plug down about 4 inches, and within an hour the rack was cleaned 10x better. I only saw the Powder Brown Tang eating it, but I'm sure the Kole Eye assisted as I see that one eating off the glass and other rocks more.
Excuse the crappy photo, didn't think enough to do a before and after, but trust me these are a ton better.