I know a medication called tetracyclin was reccomended to me to fight guppy disease(since i could not find ANY of the meds mentioned in the second article ferrikins mentioned). I didn't work extremely quickly with my tank.I found once a guppy got a signof the disease, they couldn't be cured, they only help host the parasite more. What did work was euthanising the victims right away(using clove oil is very humane way) before it spread further. Then i took out all my healthy guppies, put them in a temporary bucket while i cleaned out the WHOLE tank, top to bottom. Gravel, filter, glass everything was cleaned out with hot water. I cycled the tank with some of my used water from other tanks. No signs of it after that for me. Keeping your water clean is the best treatment for preventing any disease.