Total Dissolved Solids (TDS) tester - Primo is a rugged and reliable pocket-sized tester that offers quick and accurate readings. Primo is used for testing total dissolved solids (TDS) in applications such as hydroponics, drinking water, reverse osmosis systems, and aquariums. This meter features Automatic Temperature Compensation (ATC) and automatic single point calibration at 1382 ppm, providing a fast and dependable way to measure the TDS of your sample.