Once my Guppy had some unidentified disease, and I thought she would die before I knew what was wrong. But after a few salt baths, she was perfectly fine. So, tell your friend to try a few salt baths. They're sort of a natural cure for many diseases. Put the fish in, say, a gallon of water with several Tbsp of aquarium salt (Not table salt), and leave him in there until a) he shows signs of distress--having trouble staying upright, or b) the fish has been happily swimming around in there for waaaay too long (letter b will probably end up happening as Livebearers love salt). Add more salt the next time in the case of letter b. See if he gets better after several salt baths.