Tangs in general are always aggressive to any new fish put into a tank. The more like themselves the more aggressive, IME. That being said, once you get past the original aggressiveness due to adding a new fish, they tend to get along fine, also IME. So when addding a new fish there are a few tricks you can try to eliminate the new fish aggressiveness.
Here are ways I have tried:
1. Rearrange the rocks. That re-sets the fish's territory, and they start out on an even footing.
2. Put a mirror on the side of the tank. The established fish will spend his time fighting his own reflection rather than bother with the new different fish.
3. Use an acclimation box. This allows the fish to see each other and get used to each other so when you finally let the newcomer out, the older fish don't see him as a newcomer.
4. Add a large scary object to th etank, like a fish net or other that will scare the old fish but give a refuge to the new fish to hide around.
5. Add a piece of egg crate to divide the tank . This is basically the same as an acclimation box.