Yes, all of that... I think that in the past I've been guilty of discarding un-exhausted fixer. I want to use it to exhaustion and think about silver recovery. If I use it to exhaustion, as determined by testing, will I be able to count on using the same fixing times for film and and paper right up to the point of exhaustion or do I need to make any adjustments as I approach that point? I'm assuming I can track how many prints/sheets/rolls it takes to reach exhaustion for film and for 1st and 2nd print trays to establish a baseline so I can track how close to typical exhaustion I am and to then test. What insights can you folks share on this subject?