Bluelab EC Pen - Temperature Compensated Digital EC TesterBluelab EC Pen Temperature Compensated Conductivity Tester A meter to measure the strength of your nutrient solution is one of those really necessary items for enthusiastic hydroponics growers. Bluelab's EC Pen features the same robust build quality, accuracy and reliability that make Bluelab testing equipment the default choice for growers across the world. How the Bluelab EC Pen Works The Bluelab EC Pen measures the electrical conductivity of your