pH meters must be regularly 'calibrated' (i.e. adjusted for accuracy) using standard pH buffer solutions which are made to an internationally agreed recipe:
Flairform’s buffers are formulated with NIST* specified ingredients.
Stabilised to resist algae or growth formation and provide exceptional shelf-life.
Available in 250ml and 1L.
It is essential to calibrate using at least TWO pH buffers. These need to differ in pH by at least three pH units over the pH range being used. For nutrient solutions, pH buffer 4.0 and 7.0 are the ideal calibration standards. Some manufacturers claim that their pH meters require calibration using only pH buffer 7.0. Professional practice however, stipulates using two buffers because this will confirm or otherwise that the correct calibration “slope” is being obtained i.e. that both the electrode and meter are ranging correctly.