They are hard to find, and expensive when you do. Tangs in real life are mainly schooling fish, and they roam all over the place. Territoriality therefore I think is largely an aquarium phenom. The key here is adding small fish, at the same time, and keeping h2o qualitly high, while allowing everyone to have acccess to lots of high quality foods. Multiple algae clips is what we are talking here, and if it were me, macros grown in sump to feed out.