I dont know either but I have a Coralife Super Skimmer on my 58G and my Xenia is growing like weeds about 6 inches from my MH light. No one really knows why it lives and dies in tanks that are similar.
I agree. I have heard low light and high light. Dirty water and clean water. Then you hear of people that have it for years then all of the sudden gone. I guess that is what makes this hobby interesting. If it all dies and you want to try some more let me know. I have the white / pinkish pom pom type.
I read a article in an older TFH mag that said sometimes xenia just meltsdown. They said there isnt any proven reason but they do grow back after they melt so it should be a huge loss. They also grow more whent the melt.. This is out of TFH though so its up to you..