Okay so I have a fish and invert only tank, no live rock or coral. I have an occelaris clown, a blue yellowtail damselfish, a convict blenny/engineer goby, bumblebee and cerith snails, along with with a Valentini puffer.

I had an amazing emerald crab before he died (his name was Oz, because of the Wizard of Oz and him being an emerald crab. sorry off topic) so, this new emerald arrives because I loved the first so much. This crab is green and definitely is an emerald crab, but he is massive! He could probably catch everything in my tank if he/she wanted to. I'm especially worried about my convict blenny because she sleeps in her tunnels and is very low-laying. I can't take the emerald back to the store, and I have no friends who could take him. I'm not going to kill him because I stupidly am already attached to him, but I am very concerned. Oz was about an inch, and this one is maybe twoish. Does anybody have any ideas of what I should do? Thanks!
Maybe a better question is there any way to keep this crab tame? Or docile it out by making it fat and lazy?