YES. A 5 gallon tank WILL NOT give them the proper temp gradient they need, that is to say they need like 80 degrees at one end and ~93 on the other. IMO I don't think that BPs of any age should be housed in anything smaller than a 20 Long tank, but some people have had success keeping babies in 10 gallon tanks. Not to be mean, but I think putting a baby bp in a 5 gal is just dumb considering the temp situation, and the fact that they'd outgrow it in less than a couple months. Get him in the 20 gallon, and swap a 50w bulb to make up for increased space. The 40w should be alright for now but I'd bet that it would get the warm side temp over 85-90 at best.