Drip kalk at night to maintain slightly elevated PH (8.4) and alk levels.
I can literally turn my Xenia's and cyano growth for that matter, on and off doing this.
The anecdotal evidence for this is overwhelming where my system is concerned. Over the past couple years the system has been up I have discontinued nightly kalk drips on three occasions and like clock work a week later my xenis go "puny" on me and cyano begins to grow.
Other tank inhabitants seem unaffected by these slightly elevated levels. Needles to say setting up a nightly kalk drip is a chore that no longer gets neglected.
But then again that's just me. I am sure someone will think I am completely wrong. Such is the nature of the hobby.