What are the current parameters of the tank, especially alk? Have you tried moving the xenia to a different spot in the tank? These guys are sometimes hit or miss, sometimes unable to grow in some systems for...whatever reason. Even the reason they pulse is sort of a mystery...where the last theory I read is that the pulsing helps with oxygenating the water around them...so I'd want to try a spot with different flow to see if it perks up.