Shell dwellers rule. In a tank that size it's definately the way to go. The calvus would be fine in a tank that size. They take years to get big. I mean years. I had mine for 4 years before I had to get rid of my fish. I moved to another continent. It took several years before it was decent sized. Super cool fish, my favorite. But I've had some caudo's and they're pretty neat little fish.