What's the high and low
pH of your tank? Try measuring the
pH just before "lights out", and then again just before "lights on" to get an indication of how far the value swings at night.
Xenia are pretty sensitive to
pH swings and I've read or heard that anything under 8.3 can be generally bad for them. I think Anthony Calfo's coral prop. book is where I read the 8.3 figure.
