Mine is about 3 inches and is quite calm. I think this is because my other tang ( sailfin) is about an 1/2-1 inch bigger. If you get another tang I would get a "calmer" larger tang. Or remove the tang while you introduce a new one then reintroduce the purple after the other tang is comfortable in the tank. Like I said I think my sailfin keeps my purple in line since it is larger. Anyways good luck and hope it works out for you.