They are correct here, nitrates don't disappear. That 1-2g top-off would just dilute a little bit, but you should still have nitrates. If you really had high
ammonia levels, you should be reading levels of at least 20ppm for nitrates IME. Go have your LFS
double check these readings to eliminate the possibility of a faulty test via either bad test solutions, or user error in the testing process. Even so, with just two weeks as I said in your other thread, you are probably not cycled. Cycles with fish tend to be longer due to the amount of water changes needed to keep parameters in safe ranges for fish.