In most cases calibrating every 6 months is fine.

To do this empty the calibrating solution into a clean cup that has been rinsed in RO water and allowed to dry. Make sure the probe prongs are orientated correctly inside the T as per instructions. Place the T and probe into the cup and give it a gentle wiggle to release trapped air. Please note the temperature of the calibration solution is important, if the temperature is different to that stated on the bottle the calibration results will be incorrect.

The inline meters are designed to measure the TDS in flowing water. as the callibration solution is still always calibrate the unit to a value 3% higher than the solution. For example if the calibration solution is 342 then callibrate the unit to 352.

Allow to settle and adjust the screw on the back of the unit until the reading matches the solution, you only need to do this on either the out or in probe rather than both.