Along w/ proper tank maintenance -ie. running GAC and replacing it approx. weekly, a good protein skimmer, and regular PWC's- IMO/IME the best way to keep Xenia healthy is by regular prunings. Some say it grows so fast and aggressively because each polyp is relatively short lived in comparison to other corals. This concept has worked for me. Even the Xenia dircetly in front of one of my sump out puts pulses though it receives much more than "enough" flow from my wave maker. As mentioned xenia are a good way to judge water quality. If somethings off they are often the first to show it. Just my .02 HTH