Room temp is perfect for them. The bullhead will definetely out grow a 55gal after a couple of years. Unless its a yellow bullhead, they stay pretty small. Or you could go for a stream tank, with some shiners, daces, or chubs and some darters and a madtom. Thats what I would do If I had the space. Just take out your curent decorations and put a bunch of smooth rocks in the bottom, and maybe a couple branches. I think they're the coolest native tanks.