How exactly does a Xenia scrubber work? I mean I know xenia takes in nutrients but how do you keep them? I am having problems with die off on mine and have had them since I got it. My xenia stays open mostly but on the top right it has lost some flesh. Its a lps xenia and when its closed its hard as a rock but when its open it looks great. The die off is driving me nuts....what can I do?