clown tangs and sohal tangs can do perfectly fine in tanks in about 265 until they get about 8-9" long then i recommend a tank thats about 96x30x24 to keep them happy
also as long as you keep them in a tank where they will be over dominated they will be fine, aka getting them at a small size between 2-3" and keeping them with larger just as aggressive fish and introducing all of them at the same time, this will keep the sohal or clown tang in a submissive attitude, it worked with my vlamingii and sohal together