Bluelab ph Probe KCL Storage Solution 120 ml or 250 ml Bluelab pH Probe KCl Storage Solution is made specifically for use with Bluelab pH products. It is designed to increase response time and maximize the life of Bluelab pH pens and pH probes. For best results, KCl storage solution should be used to store the pH pen/probe after use and hydrated monthly. Bluelab pH Probe KCl Storage Solution is manufactured to the highest laboratory standards.