poor water conditions are usually the culprit. do regular water changes. get a better antibiotic, or that eye fungus can turn into popeye. i treated my cory with popeye with clean water and maracyn plus.
Also I have found that the best quick fix for getting a fish in qt is a 5 gall bucket, air stone, and a line for a canister filter. this way nothing is ever cross contaminated. Also this makes treatment calcs a lot easier and easier to control.
well the fungus disappeared and keeps on coming back it dosent seem to be doing any harm but found it on one of my gups so i did a cold water dip and the fungus died