The ISE sensor should be stored in solution. When storing for more than 30 days, place the ISE sensor in the storage bottle was originally included with the sensor. This can be filled with buffer 4 solution. If you no longer have the storage bottle, simply place the sensor in a buffer 4 solution. Long Term Storage Temperature: 0 to 30°C (32 to 86°F)**Operating temperature range for pH sensor is -5 to 60°C (23 to 140°F) and operating temperature range for the ORP sensor is 0 to 60°C (32 to 140°F)