Here are my thoughts on how to successfully keep xenia. My original specimen was added in 2000, and it has since multiplied, and multiplied, and multiplied. I am sure there are many ways to keep this animal, so what follows is merely a suggestion based on what has worked for me.
1. Moderate-High Light. The base of my colony is approximately 6-8" under my PC light fixture. The tentacles reach almost to the surface (2" from light source). I have seen xenia growing under less light, but they do not seem to pulse as much if at all.
2. Your water needs to have some organic matter in it. I do not have enough knowledge to pinpoint what exactly they need, but IMO xenia recieves nutrition from organic material in the water. I do not use any form of mechanical filtration in my tank only skimming. On several previous occassions I tried to use filter socks continuously on my system. After about four weeks my xenia began to look poorly and did not improve until the mechanical filtration was removed. Possibly xenia feeds on particulate material. I also do not use carbon for the same reason. When the water is too "clean" the xenia does not look right. Tentacles do not expand as well and pulsing slows, stops, or is not syncronized.
IMO when the tentacles of an individual polyp pulse out of sync with each other the specimen is not under ideal water conditions. I believe this is your first indication that the water conditions need improvement. In my case though, when this happens it is time to reduce the frequency or quantity of water changes. I perform about 30-40% water changes monthly, I am balanced between too clean and just right, rather than teetering between too "dirty" and just right. Sorry I throw around the adjectives clean and dirty assuming you know what I mean. What I am trying to say is that you need to reach a balance between water that is almost 100% pure with no organic material (i.e. fresh artificial seawater) and another extreme where water has not been changed, organic materal has reach high concentrations, and/or water chemistry is out of normal range (i.e. calcium, magnesium, pH, alk., etc., etc.). Careful observation and a whole lot of patience is required. But seeing as though these animals are hardy, make small changes slowly and see what affect they have.
3. Xenia likes tubulent flow. My specimen seems to benefit from a moderate to high amount of flow (sorry subjective). I have run 3-4 powerheads on a wave timer (Occasional peaks of 1000 gph in a 30 gal tank), but have cut back to two powerheads. Just do not point directly at xenia.
4. I cannot advocate any additional supplementation beyond kalkwasser. I replace all evaporated water with kalkwasser added by a dosing pump (Litermeter). I never test pH. Other supplements may be beneficial, but I have not needed them.
I hope this helps. Before long you will be weeding out xenai as I do.
