Good question. On the label, they recommend continued weekly dosing to maintain control. This could be to control the germinating spores. AlgaeFix Marine does not kill the spores.
In my field of land pest control, almost all the chemical products used against fungus, bacteria, molds and insects will take at least 60 days to gain complete control and in many cases much longer. How this translates to the marine aquarium, I am not sure. At this point, I have been dosing AlgaeFix Marine a little over two weeks.