The perfect solution to store and hydrate pH probes. pH probes are sensitive glass instruments which age through everyday use. 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 pens and pH probes. 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.