You need to test your pH so you can adjust it for maximum growth and yield, but a pH meter is only as good as its last calibration—kind of like setting the tare button on a scale, you need to come at pH from an accurate starting point.

General Hydroponics 4.0 Calibration solution is easy to use. Pop your probe into the solution, and adjust the meter to read 4.0 and you’ll be on your way to getting the correct reading, every time.