I'm amazed the Sally Lightfoot is still there....do you have a very small clown trigger?
If so, the crab will probably disappear before long.
If you have a LOT of liverock, you can try some of the maller dwarf lobsters, which you'll never see but will still be eating any food particles that drift into the liverock.
Additionally the hated "fireworm" will often do well in a trigger tank and once they become established are very good at removing detritus.