Xenias are hit and miss. As has been said a thousand times on here, they will either take over your tank or do poorly and melt away. And nobody knows why.
I have four 4x39 w T-5s, 0 nitrates, 0.008 phosphate, and my xenia are on the bottom of the tank with moderate to heavy flow and they're doing great. IME, they will thrive in any flow. Less flow and you can see them pulse better.
I've had mine for a long time and have made good money selling and trading frags in. They are absolutely unkillable in my tank and I just recently got them under control. I have one colony isolated on the bottom now so they don't take over again. I usually put a rock or two by them and within a couple months have new, large clusters of xenia to trade in. HTH