whats just a suggestion what tank size they should be in takign into account fish size. you can't put a blue tang or any tang for that matter in a 400gallon aquarium that is only one foot front to back, there is no turning space for them. so logicly atleast a 2 foot front to back should be a good tank for a tang but shoudl also have enough swimming space that it wont make a dash and have no space less to swim liek a 120g 48x24x24. idealy a tang should be kept in a 72" long tank like a 125 or a 180, but a 200 that is 48x36 is plenty of space for them to dart around i na
a 90cm leans length wise, what fish are you looking at?