I have a 12x12x18 with a waterfall set up. I was worried about the cresteds possibly getting into the back area of the waterfall, so I wedged it into the corner of the exo terra and then used damp moss and stuffed it along the one side I could get to and into the grooves along the glass between the waterfall and behind it from the top to close up the gap. I keep one adult male in this exo terra currently, use to house 2 smaller adults together in it. Even then, it should be plenty of room for 1-2.