I have my yearling in a 50 gallon breeder (36x18x19). they don't need a lot of room and aren't that active (especially when older and especially compared to say other species). I personally prefer the 50 gallon over the 30 gallon just because I like the bigger size. You can go bigger, just be sure to provide a lot of hides (also the right size-tight, snug and low) for security. Especially if you put a hatchling or young BP in a cage/tank that big. I'm actually planning on moving my BP into a 48x24x18 size cage before the end of the year. But many use the 30 gallon (or similiar dimensions) with no problem.

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1.0 Ball Python "Aragorn"
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0.1 Rough-Scale Sand Boa "Arwen"
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