Tigereyes,
A 55 gal will ultimately be too small for a dog face. They should grow to around 12" long and maybe even more in some instances. A 55 gal is only 12" wide, so you can see the problem. The 55 gal could be used for a small puffer like a sharp nose or a valitini(spelling?). You could put a dog face in there for a limited duration, but he will eventually outgrow that size tank...maybe in 6 months to a year, depending on the starting size and how much he get's fed. I would say that a minimum size would be a 75 gal with good filtration, but if your going to add other fish then you would probably need a 100 gal. That is the size that I just started with a puffer in mind.
Good luck