Gambusia,
You can order a bag of feed with either Romet or terramycin from one or both of the manufacturers below. You can have it shipped UPS. It will probably have to be sinking feed. Romet is more of a broad spectrum feed if you don't know what bacteria is hitting them. Not sure which one has the Romet anymore. Could be another manufacturer in PA that the name escapes me at the moment.
That said what kind of environmental conditions do you have? Is your water getting too warm? Oxygen levels concurrently getting lower? Are your fish stressed for any reason? Did you get fish that were health inspected?
Even with health inspections there are some bacteria that are always present and not a problem unless the fish are stressed due to warm water temps, fast changing water temps, low oxygen etc. Even if you treat your fish and they recover, if the conditions persist that stress the fish, they will only have problems again.
http://www.zeiglerfeed.com/aquaculture.asp Silver Cup Fish Feeds
118 West 4800 South
Salt Lake City, UT 84107
801-262-2991
Best way to prevent diseases in fish it to get healthy fish in the beginning that are inspected to be free of pathogens and to provide a stress free environment. That is optimum temps of 55 to 65 F. for trout, plenty of oxygen, no overcrowding etc.
