Amazon.com: Bluelab MONGUA Guardian Monitor for pH, Temperature, and Conductivity (TDS) Measurements in Water with Easy Calibration, 3 in 1 Digital Nutrient Meter for Hydroponic System and Indoor Plant Grow White :
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Amazon.com: Bluelab MONGUACON Guardian Monitor Connect for pH, Temperature, and TDS in Water with Data Logging (Connect Stick not Included), Nutrient Meter for Hydroponic System and Indoor Plant Grow White : Industrial