Nunnie's article is just wrong.
Of course the ICH shows up when they add new fish. That's where it CAME FROM. It was ON the new fish, not lying dormant in the tank.
ck/Ich is always present in your tank, in your fish. Stress is the main cause of Ick/Ich. Your fish can get stressed as a result of many things. I have found that Ick/Ich seems to show up most often when I add new fish to the tank. Almost every time I bring a fish home from the store and add them to a tank within a few days not only does the new fish develop Ick/Ich, but several of the other fish as well. Very frustrating.
Of course the ICH shows up when they add new fish. That's where it CAME FROM. It was ON the new fish, not lying dormant in the tank.