I'm getting tired of mixing up new rapid fixer after I find out my old fixer died. Sometimes I even have to go back and re-fix the last roll just to have peace of mind about it. I'm starting to wonder, why can't I just add a certain number of mL of fresh concentrate to the bottle so that my fixer never goes bad at all? I use replenished developer and add 23 mL of replenisher every roll. Doing the same thing for fixer seems natural.