although your 8 week method Is tried and true there is new research stating that If no new MI is introduce into an infected aquarium, the MI already there continues to cycle through multiple generations until about 10 to 11 months when the MI has ‘worn itself out’ and becomes less infective. A tank can be free of an MI infestation if it is never exposed to new MI parasites for over 11 months. It worked for me however I did things a little different I got the infected fish out of DT when he had white dots showing then treated him with nox ich for 14 days in QT put him back in DT and never saw ich again that was 2 years ago.