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.