I have successfully used Zerotol that was over 2 years old, but I haven't found its official shelf life. I still have that batch, which will be over 3 years old now and will see how effective it is. Oxidation is the main enemy of this chemical formulation. I'll contact the company and report back when I find out anything. I have had a quart last me for 2 years in the past, as Zerotol 2.0 only requires a table spoon and a half per gallon of water. There is a new Zerotol product that is greatly diluted for home gardening use, but I have no experience with that product.If I buy this how long is the shelf life? Most nutrients shelf life is 2 years from opening.