The BL983319 is a compact, panel mounted, process controller for measuring total dissolved solids (TDS) in a process stream that is within the 0 to 1999 ppm (mg/L) range. The device features a large LCD with protective cover. Users may choose from automatic or manual dosing modes. When in automatic mode the dry contact relay is activated when a reading is below the set point. The relay can be used to supply power to a dosing pump to add fertilizer to a nutrient solution in order to maintain an ideal concentration.