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For a newly added coral this can often be the case. Leathers will close up and go dormant for a bit as they adjust. It is a process refered to as sloughing
in which the leather will end up shedding and "renew" itself. Should be back to normal in a few days or week sometimes.
I would suggest listing some specs on the tank with water paramaters to be sure nothings amiss there. Even though this can be a normal occurance, no need to take chances.