If you choose, you can make your own pH Storage Solution. It requires creating a (or using a pre-made) pH 4 buffer solution and then adding the appropriate amount of potassium chloride.
This video can help guide you through the process.
If in doubt, we recommend using our pH Storage Solution but in either case just be sure to keep your pH electrodes in solution when not using them. If they do dry out, follow the instructions in the manual to rehydrate the glass membrane.