It' pretty easy to maintain 60% to 70% humidity and even higher in a room with quite low ambient humidity. Racks are tougher than tanks, but a plexiglass cover (with about thirty 3/8" holes drilled on the warm side and about half as many on the cool side) placed on a tank, with a small water bowl in the middle, gives me about 65% in a room with an ambient humidity of about 40% to 50%.