I had one of these in my 29 gal
reef tank. He did NOT just stick to weak/dying fish. He ate 2 fire gobies, 1 green mandarin, a watchman goby, several peppermint shrimp, several blood shrimp, several coral banded shrimp, and two arrow crabs. Of course, it was a small tank, but I fed him every day religiously and he still couldn't resist the fish. I did have one peppermint that survived for over a year, and one arrow crab the same. The cool thing with the lobster was he would molt and if I was quick I could pull the molts out and let them dry on a shelf, so now I have about 10 little lobster shells from the four years I had him. I think in a 55 you might have a better time of it... but the hermits will probably be lobster snacks eventually. Then again, FWIW
, maybe mine was just super voracious.