These powder packs contain premeasured unit dose reagents suitable for use with Lovibond/Orbeco-Hellige colorimeters, Aqua comparator test kits, YSI, Thermo, and Hach® instrumentation/test kits. Reagents for chlorine are DPD chemistry. Some parameters require multiple reagents and are bundled into a "Reagent set", which can include powder packs, tube tests, or both.