Years ago, I got in a group of leopoldi and their shipping water was really contaminated with ammonia. I made the stupid mistake of doing a plop & drop in water that had the same ph, hardness, etc. I WAS VERY VERY STUPID for doing this!!! By doing this, I burned the fish and they all developed fungus. I was out of my mind!
The advice I was given was to do 3/4 daily w/c and administer salt. Keep your aquarium temp. at least at 96° F. The fungus would fall off and regrow, but each time the burns got smaller and smaller. Eventually they were completely healed. *I used no other antibiotic or remedy with this treatment. But... other treatments may work better.
Now you have to be careful with using salt for some salt will keep a fish hydrated and some some salt may cause dehydration like epsom salt (magnesium sulfate - used for constipation in fish) which will expel their bodily fluids as well. It has been a long time (years) since I had to do this, but I used regular table salt. I'm sorry but I do not remember the exact dosage of salt, so maybe someone else can chime in.
You can tell the difference between fungus and a bacterial infections. Fungus will always appear "fuzzy" or "furry." If this is what you see in your fish, then it is fungus. If it is not, please reply back.