Xenia
 

I had Xenia in my reef and I Tryed everything to get rid of it. Mine grew so well that it grew up the filter tube and inside of my aquaclear while I was out of town. Never again.

What has worked for me is using the kalk paste I used to kill off aiptasia. After pulling the stalks off the rock, I put a little bit of kalk paste on the area and it makes the "burn" and melt away after a couple days.

That only works temporarily. If even a tiny bit of the flesh lands elsewhere in your tank they will just start a new patch.