True, the pH has a direct effect on nitrifying bacteria. These bacteria operate at close to 100% effectiveness at a pH of 8.3, and this level of efficiency decreases as the pH lowers. At pH 7.0 efficiency is only 50%, at 6.5 only 30%, and at 6.0 only 10%. Below 6.0 the bacteria enter a state of dormancy and cease functioning. [Kmuda, “Aquarium Bacteria and Filtration Manifesto,” Parts 1 and 2, OscarFish website.] Fortunately, in acidic water (pH below 7.0) ammonia automatically ionizes into ammonium which is basically harmless. And since nitrite will not be produced when the ammonia-oxidizing bacteria are in “hibernation,” this decrease in their effectiveness poses no immediate danger to the fish and other life forms.
Given the above (which is cited from an article I wrote on bacteria some years ago for another forum) I would not expect nitrite at all. I have never had nitrite in any of my tanks, as the pH is always well below 7, and I have floating plants and sometimes lower plants. On the level, another citation from the article:
The fastest uptake of ammonia in an aquarium occurs with live plants; ammonia can be both assimilated (as a nutrient in the ionized form ammonium) and taken up (as a toxin, NH3) by plants. But ammonia is also taken up (though more slowly) by certain nitrifying bacteria, and this produces another form of nitrogen—nitrite, which is also highly toxic to all life at very low levels. Fish readily absorb nitrIte from the water and it combines with the hemoglobin in their blood, forming methaemoglobin. As a consequence, the blood cannot transport oxygen as easily and this can become fatal. At 0.25 ppm nitrite begins to affect fish after a short period; at 0.5 ppm it becomes dangerous; and at 1.0 ppm it is often fatal.
Given the fish seem to have no reaction at all, I would surmise the nitrite cannot be anywhere close to 2 ppm. If the test is accurate, then perhaps there is some other chemistry factor at work. That takes me way out of my depth.