I just have to say there are to things (imo) that make the experience of keeping rays the most rewarding. One is hand feeding, I hand feed mine every day and LOVE the experience, I put my hand with a nightcrawler on the bottom and they come to me and suck them up like a piece of spaghetti. If the tank was too tall you wouldnt be able to do this. The second thing is watching them climb the walls, I dont know what it is but there is something about watching them stick to the walls and watch there little mouths pucker that can entertain for hours lol. Point being if the tank walls are too high, hand feeding and maintanence will be difficult, if the walls are too short they wont be able to climb the walls. My tank is 24" high and for now its perfect but my rays are small. They wont be small for long and I'll have to move them to a bigger tank but I think 30" will be my max.