20 gallon is fine, but just make sure that these snake(s) have room to climb, since that is what they do most of the day. also, i would say like bark chips, exo-terra makes them and they are treated for mites, so that just makes them better. they might hold in some humidity also. btw use brown furnishings so that you actually know where the snake is, because if you use green, it will be very hard to find your snake. but besides that, are you sure that you want a rough green, because many of them are jumpy, VERY delitcate, hard to breed, and hard to get eating. but if you are willing to accept that, then go ahead. im just saying that those are the facts and you may just be makeing frustration for yourself
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i have one Brooks Kingsnake, hopefully breeding in the next couple of years! yaaahhhh, only if i can find a male though lol, but im still looking for a male lol