I've had the neons for about a year... I got them when they were very tiny, so they are all still pretty young. About a month ago, I moved them from a heavily planted 10 gallon to a new 29 gallon. Since I was using the same filter media and plants, the water parameters have been petty stable. The temp is 25/77 degrees. GH 75. KH 80. PH 7.2.
After noticing the growth on the neon's mouth, I dosed the tank with Paraguard (the only medication I have on hand) for about 10 days with no effect.