I have seen some strange things when mixing tangs. I attempted to add a powder brown and blonde naso to a tank with an established koi and sailfin. The koi immediately attacked the powder brown to the point where I had to pull the powder brown out and ended up giving it away. It took to the blonde naso fine within a short amount of time. Several months later I added a small blue hippo tang and experienced no aggression why so ever. This leads me to believe if the size of the new tang is very different and of a different genus your chances of success are much higher. I also do feed heavy a mixed diet of mysis shrimp, rods food, algae, flakes, garlic xtreme, zoecon and reefroids. Soak it for 30 mins prior to feeding. Also a sheet of nori a day.