In order to keep your ph meter as accurate as possible, you will need to calibrate using three of our pH buffer solutions.

pH Buffer Solution - 3 Pack (4.00 / 6.86 / 9.18)
In order to keep your PH meter as accurate as possible, you will need to calibrate using our three buffer solutions. 
We would strongly recommend if you haven't used your ph meter in a while to always use a buffer solution before you start your brew.
If you do not have any, we would also highly recommend you use this solution for storage after every use.
Directions for use:
1. Completely empty the powder into a clean 250mL glass beaker.
2. Add 250mL of deinoized water to the beaker.
3. Stir until the powder has completely dissolved.
pH solution is accurate to (- ) 0.01pH