I freshwater dip my Xenia for about 1-2minutes. It killed the worms and it also almost killed my Xenia.
The next day, half the polyps didnt expand and those tentacles melted off. The main branch also drooped and I noticed some skin peeling off.
I used iodine supplement every day 5ml (on my 140G tank) everyday for about 5 days now.
The Xenia seemed to be back alive and gaining health too. I hope those melted tentacles will heal and wont spread any further rottings.