Crabs have claws for a reason.
Sometimes they just use them to pick at algae - good thing.
Sometimes they use them to kill other clean-up crew critters - bad thing.
Sometimes crabs are angels and never bother anything you don't want them to.
Other times - look out - they may go on a killing frenzy.
That's what crabs do. Not all of them, but some of them.
Species is not a 100% sure thing as well.
Crabs are unpredictable.
I like them though
![Wink ;) ;)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
and if they kill something in my tank - well so be it - they're doing what they do.
Sally Lightfoot ate my coralline algae - it was not welcome any longer.
Snails - can't go wrong with most species.
Shrimp - Banded Coral / Coral Banded can be mean little guys.
Peppermints & Cleaners - I've never had a problem - they are whimps. Peppermints seem to hide all day - come out at night.
Cleaners - gotta love the cleaners. Active and beneficial IMO.
I like to load up on snails for the major cleaners.
Scarlet hermits I like, and I've got some "killer" blue legs I'm considering giving away. Nasty little shell stealers no matter how many shells are available to them - they want a shell that's moving - and they will do what they must to overcome the current resident.
I also like to keep at least one black brittle star in my tanks.
Never had a problem with these guys ( that I know of ).