Fish Harmonizing

[Karsten]

Hello all. I have a question about how to add new fish into an existing system. I have heard to add new fish at night or move rock around to change territories. Is there any other methods? Every time I add a new fish to my system the other fish pic on them. Sometimes they get over it and become part of the family but other times I have had to rescue the fish from certain death. My tank is in perfect harmony right now but I would like to add new fish. Any advice would help thank you.

I have Tangs, and Anthais at the moment.