I might me wrong, but has always worked for me. I had a Naso in one of my tanks for about 6 months, he was qt before he was added to the tank and was the only fish in the tank. One day I come home and he was covered in ich, found out the tank had overheated. So where did the ICH come from, when the tank was ich free and he was qt for 8 weeks before he was added to the tank?