I think growing xenias is somewhat of a mystery.
Lighting is only part of the equation when it comes to growing Xenia or Anthelia. Sometimes they grow, and other times they just melt away and die. In my tank they grow in waves, or seasons. At one point they grew on everything, across the sand, on top of dead snail shells, on the back wall glass, pretty much everywhere. Then after a while they would suddenly die out. Right now they are on a die-out phase in my tank. Although I've been trying very hard to scrape them off of everything and kill them.
I remember reading that dosing iodine helps them to grow as well.
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