I have a colony of Xenia that I introuduced into my tank recently. They are taking off like wild fire. The colony has grown to the point where they are beginning to touch some of my SPS corals (hydnophora and acropora). I haven't noticed any sort of damage, but I am wondering if it is healthy to allow these two organisms to touch. Some of my xenia came into contact with star polyps and lost the battle. What is the rule of thumb when it comes to aggressivness with xenia's? Any thought's on this?