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How Nitrite & Nitrate Testing Works

        The most common nitrite test kit is one that is based on the Griess Reaction, or a slightly modified version of it. With this type of kit , you place a known volume of aquarium water (usually 4-6 milliliters) in a clear test vial. Three to eight drops of an acidic sulfanilamide reagent is then added to the test vial. This is followed by the addition of three to eight drops of N-1-naphthylethylenediamine dihydrochloride solution (NED for short). After ~5 minutes, the resulting color of the solution is compared to a color gradient nitrite chart to determine the concentration in either ppm-NO21- or ppm-N(itrogen) [ppm = parts per million and is equivalent to mg/L, milligrams per liter]. Variants of these types of kits also exist in which the liquid indicator is replaced by a powdered, granular, or tablet form of indicator...............

        The most common nitrate test kit is one that uses cadmium metal to reduce the nitrate (NO31-) to nitrite (NO21-). The resulting nitrite can then be tested in a similar way to that described previously. With this type of kit, you place a known volume of aquarium water (usually 4-6 milliliters) in a clear test vial. Powdered cadmium metal and sulfanilamide (or sulfanilic acid) is then added to the test vial. This is followed by the addition of NED or some other reagent (sometimes gentisic acid) that will form an azo-dye. After ~5 minutes, the resulting color of the solution is compared to a color gradient nitrate chart to determine the concentration in either ppm-NO31- or ppm-N(itrogen). Variants of these types of kits also exist in which the liquid indicator is replaced by a powdered, granular, or tablet form of indicator................

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