The Bluelab Conductivity Pen simply tells you that your plants have the right amount of nutrient in your solution and lets you know if adjustments are needed. To feed plants well, we need to know what we’re feeding them. Start with a quality nutrient. Measuring the conductivity every day is the best way to avoid over-diluting or over-concentrating your nutrient solution. Completely change the reservoir solution every 7 days. Top up the nutrient level between changes – so your plants always have the right amount of food. The Bluelab Conductivity Pen also measures the temperature of the solution, as root health is vital to the success of a crop. Temperature affects the growth rate and structure of a plant so a solution temperature of 18 – 22˚C or 65 – 72˚F is recommended.