The 20 ml Hanna 35 ppt Salinity Calibration Solution Sachets are top of the line 35.00 ppt salinity calibration solution contained in convenient portable single use sachets. The NIST traceable packages are expiration dated and last for 5 years and boast light block foil to ensure maximum freshness every time. Designed to be used directly with the Hanna Instruments Marine Salinity Tester..