I have many mixed genus of tangs and they coexist very well but I also have stocked in order of aggression.Which tangs of the same species can be kept together (as a group of 5-7) in captivity.
Tank is 84*32*25
Years ago, I had 5 chocolate Tangs together ( LFS had them and no customers wanted them, so I got a great package deal for them all)… I think that they were in my 300g.
Eventually traded them out to get some more colorful species.
Recently picked up another for my next (and last) tank move.
I have never had a problem keeping any tang with any other as long as they have ample places to go away and hide and are fed well enough that they are growing well. I have no disease stress.
Most people do not feed them enough or have caves and arches and other things for humans that are not good for fish to feel secure like stacked up rock where they can totally escape and hide fully.
I have 2 purples in together right now - one about 19-20 years old and fully grown and the other half that size. I once had 3x black tangs given to me that ate acans that got along fine - they were quite large. Multiple yellows were no problem either.
I have many mixed genus of tangs and they coexist very well but I also have stocked in order of aggression.
Ive seen lately groups of purple tangs but over the last few decades- Yellow tang, convict tang, hepatus tangs and orange shoulder tangs
I'm not an expert but I did get some advice from an LFS owner that specializes in only fish that stuck with me. He said if you intend on having a small number of tangs, make sure they are all part of a different group (body type), such as Zebromosa, Paracanthurus, etc. There are 4 in total, where only the Blue Tang occupies the 4th spot. If you intend to have several of the same Genus (like multiple Zebromosa) then you would need at least 3 to disperse the aggression.
I only have 3 tangs, a Yellow, a Whitetail Bristletooth, and a Blue tang, and have no problems. Sometimes the Yellow tries to attack the Bristletooth, but it's short-lived and not something I worry about.