When I buy chemicals I write the date I bought it on the container with a permanent marker. When I open it, I write "Opened" then the date I opened it on the other side. I like Ilfosol, but the darned stuff is like dust in the wind!!! If you are not shooting a lot, it goes south pretty quick. I think 6 months is tops for it. I keep the open bottle 'squeezed up' as much as I can & really ream the lid down!
Hope this helps some!