who is talking about animal activists. I did a 5 min search on the Internet, first on the PB and this is what popped up as an average opinion
"Minimum tank size: 100 Gallons
Behavior: This species is of average hardiness, at times being a little difficult when first introduced into the aquarium environment. Once settled, this species should do well for the aquarist over a long period of time. The Powder Blue Tang is a very shy fish, it needs many hiding places in your aquarium. It can also not be kept in aquariums with aggressive fish and with aggressive eaters, not even other tangs exhibiting this behavior. The powder blue will always be out competed for food and will, eventually, give up trying to eat completely at all going into a "starvation mode," leading to quick and serious deterioration.
Cautions: The Powder Blue Tang can be somewhat aggressive towards other tang species so it is not recommended that you mix this species with other tang species unless it is in a large aquarium environment. Keep only one per tank. "
the sohal was even better
"Minimum tank size: 180 Gallons
Behavior: Can be a very aggressive fish, often nipping at and harassing other less aggressive tank mates. Additionally, it is extremely difficult to keep this species with other tang species as they will constantly harass each other, often until the death of one of the fish. However, aggression may be lessened in a very large aquarium. "
a few other sites suggested 100 gal as a min for the Sohal but recommended bigger.
so going by what is out there and freely available for information and I will go with the smallest recommendations I found to have those two tangs you should have a min of a 160 gal tank, but you have 3 tangs in there don't you?
Personally I could care less what you do with your tank, but don't try to justify your self to us when we ask about a possible problem with rhetoric about how you are some miracle worker with aggressive fish. If you cared so much about them to spend that much time to make sure they don't kill each other you wouldn't have put them in the same tank to start with.
Steve