general rule of thumb is that the aquarium should be at least 1/2 or 2/3 as long as your snake(depending on who you ask those are the most common numbers you get), and anything much larger than the length of your snake has the possibility of causing them stress(they like smaller spaces) but is not the case with many snakes who can be happy in larger enclosures if there is enough cover.
55 gallon aquariums are hard to keep humidity levels in, but sometimes you just have to work with what you have.