Bluelab� pH Probe KCl Storage Solution is made specifically for use with Bluelab� pH Probes and Pens. It is designed to increase response time and maximize the life of Bluelab� pH Probes and Pens. Add KCl solution to the cap of the pH pen/probe for storage, after use and hydrate in KCl solution monthly. Instructions are on the label of the bottle. Bluelab� pH Probe KCl Storage Solution is manufactured to high laboratory standards. The perfect solution to store and hydrate your Bluelab� pH probes or pens.