Sad news. That crab turned out to be an assassin. Saw him the other night munching on a chromis. Tried to spear him with a tong but missed. He lost one claw. I thought he would not be able to hold on to a prey fish with just one claw (wrong!). Last night saw him again, tried to spear him again but he went inside a rock. Took that rock out of the tank and placed it in the vat with extra rocks. This morning, saw another chromis with a huge gash in the underside just past the cloaca, almost half way through his body. Anyway, checked the rock a few minutes ago, the crab was dead. Turned out the water in the vat was very high in salinity. Here is the convicted murderer!!!