Hi! We just got back from a week of vacation and I came home to find one of my neons with a strange white patch on its upper mouth. He's still shoaling with the others and he's eating fine. He's in my 54 gallon. Ammonia and nitrite are 0 and nitrate is about 5. I'm about to do a water change, but I also wanted to get any ideas on what might be going on. I had someone come over and feed them three days while we were gone and I premeasured all the food into labeled containers.