They melt in my tank, while acros, LPS and zoas do fine. They can be ticky. They seem to like dirty water (many softies like more nutrients for more growth, or at least this seems commonly accepted) and low/medium flow. They will do okay in higher flow, but increased flow seems to reduce pulsing. We can find you another xenia for a lot less than $30
. In your tank, they should do well.
How long had it been in your tank? If it was recently shipped, the stress involved could be the cause. They secrete chemical when shipped that can 'suffocate' them. People are figuring it out now, though (blasting with a powerhead and allowing the 'slime' to rinse off prior to putting in a bag seems to inprove shipping rates).
Many softies seem to like a little Iodine from time to time. On a tank as small as yours, I'd be very careful, though. A little goes a long way. I don't test for iodine, so I only dose half of what it says about .75X as frequent in a 125.
Did you get a temperature spike, possibly?
As for xenia, Casey (greystreet) has some pink pulsing and coralreefing can get you some blue pom poms (they are my favorites because of growth form-easier to control).