This will most likely sound crazy but I would like the opinions of our experts. (Let it be known, I do not consider myself one!) I have been keeping freshwater fish as a hobby for as long as I can remember. I'm 63 and have had an aquarium for at least 40 of those. As I posted some time ago, back in the day I never heard about cycling a tank. We just set up the aquarium, removed the chlorine from the water and added the fish. I've always had good luck with them. After being away from the hobby for a few years because of some life changes I decided to get back into it. I now have a 72 gallon bowfront and I'm loving it! Yes I did cycle the tank and have had much success over the past 4 years. Simply put, I've learned a lot from this site! Now getting to the point. years ago (in my teens) a friend and I would frequent a tropical fish store in Paterson, NJ. At the time this guy was the know it all when it came to keeping fish. When it came to treating diseases he said to put copper pennies (1 per gallon) in a nylon sock and hang it in the water for 24 hours. He claimed that copper killed all diseases. Has anyone else ever heard of this?