that is what we need to figure out, something is obviously is not right and stressing them out. But right now you gotta treat their noses, because untreated it might go to septicemia = death. fecal test gotta be done to rule out possible problem here. and step by step we should get out of all "possible" until we solve the problem. age might be a factor here too, with age body resistance to certain things are going down, same as for any other species I'd think. please don't get offended by questions, I'm trying to check out all points that might have caused this.
what type of light bulb exactly are you using, what percentage of UVB?