I would stick with Zebrasoma tangs, IMO they're the hardiest and least disease resistant of the Tangs. Also, they seem to adapt better to a little less wimming room. On the other hand be aware that many of them will eventually outgrow a 90 gallon. If you know you will never upgrade from the 90 the Ctenochaetus Tangs stay smaller for the most part, with some of them having a max. size of about 6".