When I first got my Pom Poms they pulsed well. Description of my tank is on my website, tells you everything about my tank. Every single one of my corals do well in my tank, growing, etc. The Pom Poms did well but grew slowly for about a month. And then, without me changing anything it is slowly starting to shrink. I predict it will die sometime soon, but for now it's hanging on. I use I.O. salt, and only dose SeaChem Reef Iodide once a week (A very small dose compared to the directions).
The only thing I can think of making the Xenias grow in the negative are the other soft corals in my tank. I am thinking that the warring chemicals are too much for the Xenia, even though I run 3/4 cup of carbon in a Phosban Reactor.
The other aspect is that my tank may be a bit too clean for the guys. I run quite a bit of carbon for my tank, plus a skimmer, and do water changes about once a week or two. I also have an AC 110 but it only has rock rubble. Who knows. Oh yeah the Xenia pulsed for the month but then slowly started stopping and now it pulses maybe once in a blue moon. HTH