The test will also respond to nitrite but in normal situations nitrite levels will be very low compared to nitrate. To correct any effect a nitrite test can be carried out and the result as N subtracted from the nitrate result as N
Fill a nitratest tube to the 20 mL line with sample.
Add a level spoonful of Nitratest Powder.
Add a Nitratest Tablet. But, do not crush.
Replace screw cap and shake well for 1 minute.
Allow tube to stand for 1 minute.
Gently invert tube, three times.
Stand tube for 3 minutes or until complete settlement.
Remove cap and wipe rim to remove all traces of Nitratest powder.
Carefully decant 10 mL of clear liquid in to a photometer tube.
Use this to "blank" the instrument. Place in cell holder and press Blank.
Then, add a Nitricol tablet and crush and stir.
Place in the cell holder and press Measure.
Allow timer to count down 10 minutes. Concentration of Nitrate will then be displayed.