pH BUFFER 4 and pH Buffer These are solutions of known and exact pH. If your pH meter doesn’t read pH 7 (or pH 4) when the probe is put into the buffer then the meter is wrong and needs calibrating. We recommend that the meter is checked with pH 7 Buffer at least once a week, and checked with pH 4 buffer at least monthly. Each pH meter comes with instructions on how to calibrate the meter. Pour enough buffer from the bottle to cover the glass end of the probe when calibrating, and discard the solution after. It isn’t best practice to return used buffer to the bottle it came from. Correct pH of hydroponic nutrient solutions is … Continue reading pH Buffers