Calibration

Standard reference solutions are used. The bottles are marked with the conductivity (EC) value in milliSiemens/cm and the corresponding ppm values for sodium chloride (NaCl) and potassium chloride (KCl) solutions, and sometimes for a “442” reference mixture. The conductivity of sodium chloride solutions is close to that of hydroponic mineral nutrients, so a “1000-ppm NaCl” standard is most frequently used when calibrating the meter for hydroponic solutions. You should follow the calibration instructions in the manual, which the manufacturer of your meter provided.

The electrical conductivity (EC) of your nutrient results from motion of mineral ions when the meter applies an electrical voltage. The ppM value of a sodium chloride solution happens to be very close to half of its conductivity value (in milliSiemens/cm), so many meters display the conductivity as an equivalent NaCl amount