I have a 5.5 gallon nano tank with just two emerald crabs and elephant snail and a baby brittle star (bred from our large tank). This morning I noticed that one of the emerald crabs was molting -- partially out of the old shell. It's been nearly 12 hours and "he" seems to have not made any progress completing the molt. Except for the other emerald crab there is nothing predatory or dangerous to him in the tank. We've had other emeralds in our large tank, but had never seen one molt before. I don't know if this is an excessively long time and indicates a problem? Should I try to help him or let nature continue to take it's course?