It wouldn't be a good idea to put a tang in the tank because sooner than later he would outgrow the tank and need a new home or live a crappy life in a small tank.
The rule of thumb for tangs (as it has been told to me) is that a tang needs at least four feet of swimming room in some direction (diagonally, straight across or back to front). If you can't accomodate that in your tank, there is no way you can have a tang.