Quote Originally Posted by gzinsel View Post
I am hoping that some savvy chemists can answer these questions. Please!!!! How do you determine your fixer capacity. is there a way to determine? with some sort of "measuring system" when it is time to make new fix? Or does every one, like me, keep a tally sheet of "so many" 810's per liter, once you reach the suggested "limit", you then pitch it, and make new? I find this to be at best a guessing game, not archival, and at worst, wasteful. You are either using your fix "beyond" sound practice, or you not using it enough and throwing GOOD chemistry down the sink!!! I hate to guestimate!!!
Gzinsel, the general consensus is that you can use fixer until the silver content reaches some predetermined level. There are several sets of published recommendations for this; for commercial work a higher level is allowed, for maximum permanence a lower level.

The problem is that it's difficult to know how much silver you've built up. This is why the general recommendation for counting the sheets. For a little better accuracy, you can purchase "silver-estimating papers." These are little test strips which you dip in the fixer, then compare the shade of the test paper to a reference; it gives you an approximate idea.

If you're not already using a 2-stage fixer, you should look into this. It lets you get a lot more use out of your fixer, with a bigger safety margin to boot.