When you say the water depth should be deep enough for crabs to submerge, you mean shell and all, right? So the water should be deep enough for largest crab to submerge completely (shell and all) and set up so smaller crabs can also get out easily. Right now, we have three crabs, (all roughly the same size - not tiny, but I would say they are still small) but we are looking to upgrade our 10 gallon tank to a 20 gallon (or a bit bigger), and I may be tempted to acquire a couple more small crabs. They are fascinating little guys to watch!
