Pen-type testers have been available for several years. . . Pen-type testers have been available for several years and are used where pH and conductivity accuracy is not critical.
More accurate instruments are usually considerably more expensive.
The two major manufacturers of pen-type testers are Hanna Instruments and Eutech Cybernetics. Eutech manufacture the push-button TDScan 1, TDScan2, TDScan 3 and the TD5can 4 conductivty meters. Recirculating hydroponic systems need to be accurately tested and adjusted as growing plants feed on selected salts in the nutrient solution. Hence, to maintain maximum growth, the nutrient solution needs to be maintained at its optimal concentration. If plants remove acid salts, the nutrient solution becomes more alkaline.