pulsing xenia dieing fast

I would TDS check your water. I recently had algae and cyanoemerging in my tank and tested my RO/DI and showed 80ppm on my TDS. I replaced my DI resin and brought my TDS back to 0-1ppm and the stuff went away. It may not be what happened with your's, but it may be worth checking. I would also test for heavy metals or chlorine/chorimine in your water as well.

 

Xenia will melt and die for no apparent reason. I lost a whole colony one time and never had a problem with anything else.

It could be the water isn't dirty enough for it because they along with Zoa's tend to do better in water that isn't completely pristine. Whats the temperature in the tank, it really prefers a little bit cooler water.

If the other stalks start to melt from the bottom like that you might want to try cutting them off above the melting part and put in a different location in the tank.