so far i have not gave them any land to get on they have just stayed under water will this harm them? they have been like that for weeks. seem to be very active. also how big will these crabs get?
They will be looking for a way out soon enough. I have never seen them much bigger than a silver dollar.
You should check out the book "The Complete Aquarium" by Peter W. Scott. There is a whole section on these crabs. It says that they make burrows in the sand. It would be interesting to see this if you had some sand on the sides of your tank. It might be like looking into an ant farm.