star coral

***SOLD*** Looking to sell these star polyp frags $10 each and give away the mushrooms for free. Open to trades as well. State college PA.

Hi All, over the past week or so a portion of my star coral has started to die off. I'm not sure what is causing it, or what to do. Nothing else in the tank is impacted. Here's a picture below -- any suggestion(s) on what it could be or what I should do? (It's the white part at the bottom...