I am currently shopping for a new tank. My betta is currently in a 4 gallon Biorb. I've been looking at Reef-One's 9 gallon Biube. It's 18 inches tall. I figure that after adding substrate and leaving a few inches of air on the top, it'll be about 15 inches deep or so. Could this be too deep? I'd assume betta fish are more accustomed to shallow waters.