Had a fowlr up for a long time. About 4 years ago I added a small yellow tang. Over the last 4 years the number of fish in the tank has decreased until 3 months ago when it was down to a diamond goby and the tang who is about 4". Tang had always been a model citizen. About a week ago my LFS had a very healthy fat 5" Aussie Tusk which is a fish i've always wanted so I got him. When I introduced him to the tank, the tang went ballistic. So i caught the tang, moved him to a QT tank. Bought some more rock and completely rearranged the rock work adding as many caves and levels as possible. After a week, I readded the tang. He once again went after the tusk to the point he keeps him pinned in an upper corner of the tank. I heavily feed and always have nori on a clip. Any other ideas for reducing the aggression? Hoping to keep both fish and add a few more down the road.