The Care and Feeding of Your pH Meter

Questions regarding pH meter storage and calibration come up frequently. Here are my recommendations for enhancing the longevity and performance of your meter and probe.

Below is a photo of the storage and calibration solutions I use for my meter and probe. The large bottle is an expired batch of pH 4 solution that I added potassium chloride to create a 1N KCl solution. Note that I cut a hole through the bottle cap so that the probe can be stored submerged in the solution. Potassium benzoate should also be added to the solution to help reduce biologic growth in the solution. (PS: I haven't added the benzoate and haven't noted growth...yet)

The other bottles in the photo contain pH 4 and 7 calibration solutions. Since those calibration solutions have a finite life (typically less than a year), it is important to replace them on a regular basis. To reduce the cost of replacement, I recommend using dry buffers such as the pHydrion products shown. There are multiple capsules of dry buffer in the small containers. You add the contents of one capsule to 100 mL of distilled water to create a fresh buffer solution that will last for about a year. Keep each solution in a small sealed container such as those shown below.

For calibration, I pour a cap full of each solution and submerge the probe in each. Be sure to rinse and dry the probe before submerging in either solution. (I use RO water to rinse and then blow excess water off the probe with my mouth and never touch the bulb). Be sure to take your time when calibrating. The meter and probe reading will vary and its best to leave the probe in each solution for several minutes before accepting the reading. Do not return the used solution from the cap to the bottle. Throw it out.

These are economical ways to keep your probe performing well and your meter calibrated.

Enjoy!