i read, and this is a direct quote from the book"aquarium corals" (please dont sue me eric!) ;indirect bright light and moderate current will allow for the best expansion and health of Caulastrea.
basic meaning dont put it in the directly under a MH, or directly in the effluent of a power head or pump.
and you say your crab is much bigger than mine? like, how big?
i brought mine to my LFS to see if i could get anything for it and the owner said telling by the black tips on the claws, that it was a menace, which i already knew, and that all he would want it for was fish food. so i took it back home and it now lives in a tall glass in my fuge where he cant excape. i found him straddling a montipora digitata frag i had, and was eating it. thats when i put him in the cup