I agree, too on the cooler temp theory for xenia. I have had a very sizable mother colony for years in my tank. I would frag it hard and it would just grow back bigger and stonger. Recently however I noticed a dramactic die off of my xenia. I could not figure out what was causing the problem until I saw that my heater was stuck on. My tank was 82 and the heater was still going. I unplugged it and the temp settled down to the 77. The xenia bounced back very well.