When using a Hach color disc test kit, what is the purpose of the viewing tube without reagent in it?
Viewing tube without reagent in color disc test kits
Hach color disc test kits require that two viewing tubes are filled with the unknown sample and then reagents are added only to one of the tubes. The viewing tube that does not contain reagent(s) is intended to be used as a blank. The blank is necessary so that sample qualities such as small amounts of turbidity and color do not interfere with the final result.