My son has finally decided he wants a tank in his room, after me nagging so I have space for another. He wants red clawed crabs, but I'd like to set them up in a species tank. Any advice? I know they need salt but does it have to be marine salt or will aquarium salt be okay? I also know they escape, and need dry places, so if I have a ten gallon tank, how deep should I have the water? If I do it with shallow water, how can I filter it? Any advice would be greatly appreciated!