I did a water change on Sunday and noticed that all of my pulsing Xenia's are gone except for one. I've had them for a year and didn't have any problems. The only thing I added to the tank was 8 lbs of live rock a few weeks ago. Is there anything that will eat Xenia's? Also, are they sensitive to any kind of additive. My Calcium is at 460, could that do it? All of my other water perameters are normal.