What value pH buffers should I use to calibrate my pH meter

For proper calibration, buffer solutions of carefully selected accuracy and pH range are required. The calibration should be performed using two buffers whose values bracket the expected value of the samples being measured. In practice many pH meters are equipped with auto buffer recognition – this requires the use of the buffer values specified by the meter manufacturer. It is essential that the difference between the two calibration buffers should be no more than 2 – 3 pH units apart. This represents 2 – 3 decades of difference in pH value (i.e. a 100 to 1,000 times increase in H+ ion concentration).