I buy a can around 5 liters of fixer concentration for paper and use as need, usually make 1.5 litter for a session.
How long time after oppening the seal that Agfa Multicontrast Fixer for paper can be still usefull. Can I use it, say a year long, making every week some fixer from concentartion.
I was able to use my Agfa fixer 5 years after I originally opened the bottle. I tried B&W at home years ago and then went to digital for a while. I returned back to film and used the bottle of fixer that I had remaining. It worked fine until it ran out.
I think your O.K. for a year with the concentrate, Kodak gives their working solutions "2 months in a stoppered bottle". I would guess that liquid concentrates of any brand will last for years, especially if you keep poring it into smaller containers.