Just out of curiousity, what makes you think you are Xenia free? I remove a butter tub of the stuff from my tank every couple of weeks and it just keeps coming back. I call it "Aquarium Kudzu." All it takes is a few cells left behind and it will grow back. Also when you remove Xenia, you always end up with little pieces of tissue floating around that end up settling somewhere and starting new colonies. You really have to stay on top of it to get it out, or at least trained. I'm actually have a bigger problem with clove polyps. They are even harder to remove because their runners grow through the crevices of the LR. If anyone wants some, come on over and we will have a polyp picking party. There is a nudibranch that eats clove polyps but good luck trying to get one.