Way back in the late 90's, I added a 7" imperator that had a maculoses, French, annularis, and a navarchus all around the same size as the imperator. The other angels were all at least 5 years established in my tank as I purchased them as juvi's. I used a tank divider and placed the imperator, by himself, in about 1/4 of the tank. Kept this divider for about a month, each week placing one angel with the imperator, and increasing the space that they would be in. Second week add another angel and increase the space and so on. This process didn't allow the other angels to dominate and possibly kill the imperator and slowly socially acclimated the imperator to the other established fish. They all lived in harmony for another, at least four years, when I sold everything because I moved to Maui to start my career. Miss my angels, they have so much more personality than any other fish.