Hi. Im my small maybe 7 gallon bowfront tank i have 2 emerald crabs, one is bigger than the other, but ne way the smaller of the 2 keeps flipping over onto its back and just kinda stays there. When i flip it back the right way it very quickly shoves abunch of rocks under itself. Can they flip back over by themselves, should i let it stay on its back instead of flipping it back over. Does anyone have any idea what is going on with it? Thanks