Bluelab Conductivity Pen (EC or ppm)With the Bluelab Conductivity Pen (EC or ppm) you'll never have to guess your nutrient concentration again. This is the ultimate solution to measuring EC or PPM, along with temperature, and dialing in your nutrient solution for explosive growth and heavy yields. Dial In Your Nutrient Solution With The Bluelab Conductivity Pen (EC or ppm) Even if you follow your feeding schedule perfectly, it's still important to double check your work by using the