Create Your Own pH Probe Storage Solution

pH probes should be stored in a potassium chloride (KCl) solution to maintain the probe's internal chemistry. It is easy to create your own storage solution if you have the right stuff.

An ideal start to your storage solution is to start with a bottle of pH 4.0 calibration solution. Expired solution is perfect. If you don't have that, an alternative would be to use distilled water as the starting point for your storage solution.

All you need to do is add the proper amount of potassium chloride to the calibration solution or DI water to create your storage solution. It turns out that there is variation in the recommendations of what KCl concentration pH storage solutions should have. Recommendations range from 1M to 3M. That M means moles per liter. So to create a suitable storage solution, you need to add between 75 and 223 grams of solid KCl per liter of your fluid (this creates the 1M to 3M concentration). Yes, that much solid will dissolve in the liquid, it just might take a day or two.

Potassium chloride is a common mineral and can be found in local retail outlets. If you can find water softener supplies, potassium chloride is often available as an alternative to sodium chloride. Just a few chunks of that stuff should make up enough storage solution for a lifetime. Another alternative is to go to the salt aisle at the market and get some "Salt Substitute". Morton is a common brand. While there are other substances in the salt substitute products, it appears that the impurities are less than about 3 percent and they probably won't adversely affect the intended use.

The final component is adding a Benzoate preservative to the solution to help reduce biologic growths in the solution. Either potassium benzoate or sodium benzoate can be added. Use the manufacturer's recommendation for dosing that preservative to the solution. I haven't done this, but probably should.

So, you can see that storage solution is easy to create.

Enjoy!