Tetra Mouth Fungus

["Steven Maier" <stevemaier at ameritech_net>]

I Posted on this a couple of weeks ago and alas no responses. For some
reason my Serpae Tetras come down one by one with mouth fungus. None of the
other fish in the tank have been affected. ( there are also at least 80
neons and 15 Congos )
I realize this is a bacterial problem. Transmission  does not seem to be a
plausible explanation due to the fact I have been running a Sterilizer since
fish death # 3. To date I have lost about 20 at about 2 to 4 day intervals.
I would feel a lot better if I had lost the whole batch the first week.
After three months of watching them go one by one it's really frustrating.
The remainng fish grow, eat well and generally look great.
Any Ideas?
Steve