There are two sensors in the return nutrient water tank. One measure electroconductivity and the other measures pH. The pH sensor is a Cole-Palmer's general purpose epoxy covered sensor. It is in the nutrient liquid and then sends back a voltage signal based on the nutrient pH. When ammonia is used in the nutrient solution it the pH increases and when nitrate is used it goes down. It measures the conductivity of the solution or its ability to conduct a current. It doesn't give additional information on specific nutrients that might be missing, just overall ions in solution.
Different crops have optimum growth under different levels of concentration.
To receive optimum growth it is important to introduce additional nutrients to the nutrient tank as they are taken up by the plant. A continuous feed of nutrients should produce better growth than a system that allows for nutrient concentration to vary in the feeding cycle. When conductivity registers that nutrient in needed, the computer control system activates the pumps on two concentrated nutrient tanks. The nutrient tank has three attached tanks which include water, concentrated calcium nitrate and the concentrated nutrient Hydrosol by Peters. When electroconductivity registers a reduction in nutrient concentration, the nutrient flow meters allow for extra nutrient to be added to the nutrient tank.