BLH are coral safe...that doesnt mean they are reef safe. That term is pretty broad and can often be misleading. Blues will not mess with corals, but the snails and other crabs in the tank...well, thats a different matter. They are notorious for killing other crabs and snails. IMO
, they should never be introduced to a reef system if Scarlet hermits are avaliable. They do just as good of a cleaning job as the blues, they get bigger, they are more attrative, and they are not nearly as aggressive.