i keep a 40 gallon tank running for feeders...when i buy them i put them in it for about a week to fattin them up and dose it with salt never had any problems doing it this way......sorry for your lose.
breeding feeders is always the way to go but i must be lucky when i didnt breed feeders before i always used to buy them from a lfs (i was new at feeding fish live food) and my oscars never got any kind of parasite or disease but that is really lucky and just a tip i dont know if you know this or not but feeder goldfish are extremely fatty and unhealthy so dont use goldfish to feed them