Nitrite is toxic and should be undetectable in any well-established aquarium. During cycling, it may exceed 20 mg/L. Nitrate is relatively non-toxic, but it is advantageous to control it to under 20 mg/L.
MultiTest™ Nitrite/Nitrate measures nitrite to less than 0.1 mg/L and nitrate to less than 0.2 mg/L in marine or freshwater. The values reported by this kit are expressed as nitrite and nitrate rather than nitrogen (to convert to nitrogen, simply divide by 3.3 and 4.4, respectively). It performs over 75 tests and contains a reference sample for validation.