What kind of copper treatment are you using?What kind of parasite?You have to make sure when you use copper you keep the copper level maintained at I believe 0.15 ppm.It should be on the treatment.Make sure your following the directions exactly.How long of a freshwater bath did you do?What fish are you treating?What are your parimeters.Copper can sometimes affect your ammonia or nitrite.I have heard of people actually picking them off of fish.I've never done it,but I'm sure Trey or Beth will be along shortly and can tell you more.I'm just trying to give you some info in hopes to figure out what has gone wrong.