fair warning. I see the apex there and what I assume are temp and ph probes. A ph probe is supposed to be kept wet. It may need to be replaced.
What should I store my pH electrode in and why ?
pH electrodes need to be kept wet in order to keep the glass sensitive part in good condition. If the glass sensitive part dries out for more than 6 months, the pH electrode will die. If it dries out for a few months, it can be regenerated by soaking into storage solution overnight.
The storage solution brings and keeps a constant ion activity in the sensing part that will assure fast response and accurate readings. Always store your pH electrode after your series of tests are done. Electrodes that are not stored into storage solution will show slow response and fluctuations in readings.
NEVER STORE YOUR pH ELECTRODE INTO DISTILLED WATER.
Many people think that pure water is good for pH electrodes. This is wrong. Pure water actually kills pH electrodes by sucking its electrolyte out of the reference chamber. Pure water is excellent for rinsing between samples, but armful for storage purposes. If you are out of storage solution, a pH 4 buffer can be used for a few weeks. Long term storage into pH buffers is not recommended as they contain phosphate.