Essentials PH Buffer 4 

It is important to realise that unless you calibrate your pH meters with Essentials Buffer 4 and 7 at regular intervals the accuracy of the pH readings will be doubtful. Serious loss of crop performance may

result, which if allowed to continue can also result in damage to the plants.

Essentials buffers use two values of 4 and 7pH to calibrate your pH testers as they are at the outer reaches of the range of pH where you work in hydroponics i.e. 5.5-6.5. It is not necessary to calibrate pH testers to any other value for hydroponic use as we only work in a small area of the pH scale.