Bro I dun have much experience in reefing but for me , crabs and fishes not a good mix.
I have one flower crab in my sump
From wild Singapore ..
'What does it eat? The flower crab is a predator. In other parts of the world, it has been reported to eat mostly slow moving, bottom-dwelling creatures such as snails and clams, and worms. It may also eat fish, shrimps and other crabs.'