Green Chromis Fish

I have two green chromis fish who seem to be acting quite odd. they won't do anything and will hide behind my filter or heater or in a top corner. I can't figure out why. water parameters are fine, and my other fish and inverts are acting normal. I have a maroon clownfish, and two small damsel fish for fish along with the chromas, and 3 snails 3 crabs and one chocolate chip star fish for inverts. Yet the chromas are the ones acting odd. Help??! Don't know if this is normal behavior..