Coral Help

[Tyreefer]

Hi, I have a 37 gallon reef tank. All of my fish and coral are doing well, except for one piece. I was wondering if anyone could help me ID the piece and let me know how I can save him. I notice some sort of slime or algae accumulating on it, but just did a recent water change. Like I said everything else is doing well so want to know what’s different with this guy (first picture)

 

[NonstopSoda]

Please post pictures in white light, we cannot see anything in the blue pictures.