Aquariums are for fish, not reptiles. you will hate yourself if you get a 40 gallon, plus unless you really provide enough cover your Bp is going to be stressed out and probably not eat. for around the same price you can get a professionally made reptile cage like these:
These hold heat and humidity in much better.
Here is a thread I wrote on them.
http://ball-pythons.net/forums/showt...With-Pictures!
Here is where you can get them: http://www.animalplastics.com/ I suggest the T8
That setup that you just described will be a world of hurt, and really is not appropriate for a hatchling BP at all.
I suggest that you give this a read through if you have not already: http://ball-pythons.net/forums/showt...ius)-Caresheet









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