acro crabs are the only crabs i allow in my systems. i totally understand where you are coming from. if i had ever seen an acro crab leave a healthy colony i would also remove them all. since they seem to stay in the colony the whole time i think they can stay.
i do not trust crustaceans either. i tolerate peps, but the have such tiny claws that they do not pose much of a theat. the same goes for ghost shrimp (now there is a highly underated cleanup critter).
Yep made the mistake of getting a hermit. He is a nasty little bugger. Within an hour of adding him he pulled almost all my turbos from their shells, tried them on and then went back to his shell. He is now in my old 12 all by himself. This is now my QT so if I ever need to use it he is going back to LFS.
all my crabs quit their jobs when they found out that prepared foods magically appear. My emralds wont touch the bubble algae and the blue legs just wait for me to feed the fish. I am down to 6 crabs in the tank. I have about 500 turbo snails that are about a cm in size. They have been reproducing in my tank very fast. I started with about 30 turbos. This week I am going to add illynasa snails