Emerald Crab is....

[ReefJunkie]

I think the white you are seeing is the calcium deposit from you 2 part dosing.

I don't think it is from dosing your tank because my crab looks the same and I dont dose anything.

Dying I think

I don't think its dying either...I've posted this asking the same thing and it seems lots of people have their crabs "bleach out", then they are fine after they molt.
Does it look like this?