This is a 500 mL bottle of storage solution for all PASCO pH electrodes. All of the electrodes ship with a small bottle of storage solution (usually 2-4 mL) which can be used indefinitely. But if it spills, dries out or otherwise needs to be refilled, this solution provides a large supply to refill those bottles.
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. The video below 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.