I see a lot of cyano bacteria which is chocking your coral, you must clean it by hand to remove the film that's depriving the coral from feeding, and then you need to treat the cyano. This bacteria tents to settle on gorgonians and leathers preventing growth and feeding and ultimately they just die, clean it as much as you can and if you can ( I see that is attached to a rock) give it an Iodine bath and placce back in the water, make sure your nitrates are on check and your Alk. is on check.