Xenia has a rep for doing that. Some say when iodine levels drop way below .06 (natural level in the ocean) it can wipe them out. Water changes may help or carefully dose iodine - too much is bad for a lot of things - it's a good way to molt shrimp prematurely for instance.
There are different types of xenia too. Some are hardy as hell and will thrive in water with high nitrates and others are kind of a 'canary in a coalmine' and will die with small fluxuations in water chemistry.
I had a nice patch going for a while and then I opened up my old I.V. doser too much and dumped kalk paste right on them. Smooth move. Over a period of days they became stark white and looked stiff. Then faded away.
Karma for joining 3reef.
