Was there anything else that took a hit except the xenia? My experience is that a dieing xenia isn't going to impact your tank, unless the tank is small and the xenia is really big. However, I also have found that once the xenia starts to go bad it doesn't usually turn around. However, if your parameters are back where they should be, and a your existing xenia starts dropping its fingers, these fingers will often take hold somewhere else in the tank. But it doesn't sound like your parameters are where they belong yet anyway. What caused the ammonia to begin with?