I'm in the recovery stages of a terrible oodinium or brooklynella infestation/partial wipe-out, leavin just 4 fish left, one of which is a hippo tang who showed first, and worst, but unbelievably is one of the survivors. He just started coming out and not laying down 24/7 anymore, and I've noticed many times, he goes over to where my bicolor angelfish is, turns sideways in the water, and the angelfish starts picking at him! He'll stay there and keep getting cleaned till something hurts him then he'll dart away but come right back. It's not all the time, but I see it many times a day. I think that's awesome! I know butterfly fish will be cleaners to huge fish and turtles in the wild, and I think I've even seen some types of large angels doing it too, but never heard of it happen like this!