I too am having the same problem with one of my guppies. I have Kanacyn but i read someplace that anti bacterial medicine can disrupt a perfectly cycled tank and god, thats all i need. So, I read about giving fish that have internal parasites a salt dip. This includes one gallon of dechlorinated water with 4 teaspoons of salt. I let him swim in this concoction for about 20 minutes. I haven't seen a difference yet.
poor timing too, I leave for eastern europe tomorrow!!
anyone know anything about Kanacyn disrupting the bacteria in a cycled tank?