Well, that's not good. That's not what happens with mine. Now that I look closer at that pic, I see that it's the entire TRUNK that's balled up. In my case, it's only the individual heads/branches that do it (though of course at night the entire thing shrinks back down into a sort of stump).
Are you testing your iodine levels? Xenia need it to thrive, I'm told (though you should NEVER dose iodine without testing for it, I'm also told) I also hear that xenia need some nitrate in the system (a reading of around 5 or so they say)
I honestly wish I understood how xenia grows to know if mine is okay. It has two stalks, and in the month I've had them, they've grown tons of new little heads at the end and the existing ones got longer. But so far it doesn't seem to be spreading or creating new trunks at all. And like, it has a ridiculous number of heads at this point.