pH, TDS and EC probes require calibration periodically to ensure accurate repeatable measurements. Calibration solutions are used to calibrate the probe. These are liquids which are manufactured specific to the calibration process.
pH, TDS and EC calibration solutions are available in a variety of units such as pH 7.0, pH 4.0 and pH 10.0, TDS 240ppm, TDS 342ppm and TDS 1000ppm. When calibrating, ensure the temperature of the solution and probe are as close as possible.