Ammonia is only detox'd for 24-48 hours before it re-binds. The product turns it into ammonium, in basic water it will become ammonia again after a time depending on how high the pH is. In acidic waters ammonia present as ammonium constantly. Ammonium is considered much less toxic to fish. Our tests test for both ammonia and ammonium, so the readings won't change even after Prime is used.
It's good if you're too tired to do a water change one night, or fish in cycling (dosed daily), but not a permanent solution.