well, i have some in a fuge with only a 15 watt pc 50/50 light and they are doing fine. i used to have lots more xenia in my first reef tank which was only PC lights and not nearly as clean as my current tank. they will move all the way to the top of the rock, but they can go crazy. i saw a 125 gallon setup once that just had a few PC light fixtures, and the xenia were bigger than i have seen in any other tank.