I would say the size would really depend on the space you have available and what you plan to do with it. If it is just for personal use you could get away with a smaller tank, if you plan on selling then larger. Shorter tanks work best as frag tanks. I would personally go bigger so there is more room for error, but I am out of room in my house which is why I don't have a frag tank lol. 48x24x10 would be about the size I'd like.