Granted I only have a 3ft. tank but the xenia is now growing on the complete opposite side of the tank from where it started and I have hydnophora between it and the rest of the tank. In short, good luck isolating it. The only time I've seen it in quick decline is when I ran the pH of my tank at ~8.6 for 2 months to fight algae. All fish and coral did fine except the xenia whithered away. Somehow it bounced right back when I lowered the pH again but it definitely had an effect.