Em crabs are hit and miss. They can be cool, or evil!
I recently had to remove my reef lobster, because something in my tank is killing off fish. No deaths since I removed him, but I also have two Em crabs kicking around in my 120g. No way to get them out except to take apart the tank, I tried it all with the reef lobster and got lucky and cornered him and got him out. After moving the complete right side of my tank.
I am moving in a month, and will have to take the whole tank down, when I do this no more crabs, no more lobsters. They are all staying in my sump with my brittle star and lobster.
For a creature that you never see, I do not see the benefit of them in a main tank. They are good for your eco system, but keep them in a sump. If you do not have get rid of them.
120 Gallon Reef
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