The EC level of your nutrient solution will influence your plants' ability to absorb water. If the EC is too high, the roots cannot bring in water and the high concentration of ions can be toxic for the plant. If EC is too low, the plants may starve from the lack of nutrients. Some plants are more susceptible to EC values out of the optimal range than others and each species has an EC threshold – beyond which, its yield is decreased. VitaLink ESSENTIALS CF Calibration Fluid has a concentration of CF 28 – EC 2.80 – PPM 1820 at 20˚C and is a necessary complement to your ESSENTIALS EC Meter. Regular calibration is necessary to maintain accuracy of your EC meter. If you are using your EC meter daily, you should calibrate it at least once a week. When calibrating, it is necessary that your EC meter and your calibration fluid have the same temperature. To achieve this, place them in the same room several hours prior to performing calibration. Available in 250ml and 1L bottles.