Originally Posted by
sufunk
Is this only when they get bigger or is this tank too small for him even now?
All anyone can offer here is opinions. In my opinion a 3' tank is way to short for a Blue Tang. The problem isn't water volume or the size of the fish, it's swimming space. Blue Tangs like most tangs, are built to swim. There are exceptions like the Kole Tang but I'd suggest at least a 4' tank even for the Kole.
Your fish may do fine and live long, I hope it does

It doesn't mean you're cruel or anything like that. You just need to be aware that any problems your tank has will affect your Tang a LOT more than if it were in a longer tank. In other words, you're fighting the odds of success.