In my opinion, unless you are trying to get rid of bubble algae, DO NOT GET EMERALD CRABS. I got a few hitchhikers a while ago on a rock full of vegetation for my yellow tang. All the crabs would do were fight and cut off the vegetation. It made so much algae in my tank and they were impossible to capture. I brought them back to my LFS and thankfully they took them. If you want to get emerald crabs fro your clean up crew, do it for the removal of bubble algae.