I had the same problem with getting rid of ich when I bought some tetras for my 55-gallon. It seemed like they would get better from the medication and then a couple of days later the ich was back. I upped the temp to 85 degrees and dosed them one more time and the ich was gone has hasn't come back. I still keep the temp at 83-84 because I'm afraid if I don't, they will get sick again. They have been doing very well since then.