from the little bits that i can make out it looks to me to be lack of lighting, the exact same thing happened to the xenia i gave to various people that only had minimal lighting (one was a LFS that has since upgraded its lighting as it has started bringing in corals)
if i remember correctly you have a Via aqua tank??? if so the answer is quite simple, get one or two more PCs and throw them in the dead space in the lid (check out www.nano-reef.com if you need some diy tips as they do it a lot over in Usa) the guys here are pretty knowledgable when it comes to techy things as well.
the xenia will recover from its present condition (the feathery look will come back and the pulsing as well