Aqua Master pH 4.01 is a standardised buffer solution for calibrating pH meters. The solution has a nominal value of pH 4.01 at 25 °C and is traceable to the NIST standard. The calibration solution is suitable for hydroponics, growing in soil and coco coir, and monitoring nutrient solutions.

A pH meter is usually calibrated with the two-point method, using both pH 4.01 and pH 7.00 solutions. Regular calibration ensures reliable, repeatable readings and extends the life of the probe.

The pH value of the buffer solution depends slightly on temperature. Reference values for the same solution:

0 °C: 4.01
10 °C: 4.00
25 °C: 4.01 (standard value)
50 °C: 4.06

To calibrate, immerse the cleaned and rinsed probe in the solution and adjust the meter to read 4.01 according to the device manufacturer's instructions. Rinse the probe with clean water after use. Do not pour used solution back into the bottle, so that the solution stays accurate.

Close the bottle right after use and store at 15-25 °C out of direct sunlight.