Hanna Instruments GroLine 5000 µs cm Conductivity Standard with Certificate, 230 mL Disease & Pest Control Some of the chelates enter Easy on pollinators and Some of the chelates enter your plants and create a downward mobility of excess salts that exit your plants and are washed into the Flawless Finish water solution When preparing your nutrient container Hanna's line of conductivity standards have been specially formulated to have an expiration of 5 years from the date of manufacture for an unopened bottle Hanna conductivity solutions have the lot number and expiration date clearly marked on the label and are air tight with a tamper proof seal to ensure the quality of the solution