MILWAUKEE MW801 Standard Portable pH / Conductivity / TDS Combination Meter (0~14pH; 0~1990 uS/cm; 0~1990 ppm)
Milwaukee MC410 PRO Total Dissolved solids (TDS) Monitor
Amazon.com: Milwaukee BEM802 Combination pH/EC/TDS Meter with 110V Power and Mounting Kit, 0.00 to 14.00 pH, +/-0.20 pH Accuracy : Industrial & Scientific