Hach reagents contain carefully prepared chemicals that react with specific substances in a water sample to produce a measurable color change, turbidity change, or other analytical response. They are used to determine parameters such as chlorine, ammonia, nitrate, nitrite, phosphate, chemical oxygen demand (COD), total nitrogen, hardness, alkalinity, metals, and many other water quality indicators. Hach formulates these reagents to ensure compatibility with its instruments and testing methods