I have processed ten 5x7 sheets of film in 3:1 TF5 fixer--three parts distilled water (375ml), one part TF5 liquid (125ml). I have tested the clearing time before each sheet after the second one, and it's still less than 30 seconds after 9 sheets. In fact it seems to clear as rapidly as it did after the second. I doubt that TF5 has unlimited fixing capacity, but I'm wondering how far I should trust the "twice the clearing time" conventional wisdom (I have been leaving the film in the fixer for thrice the clearing time for the last three sheets, just out of fear!). Do any of you have advice on how far to trust this particular brand? Again, out of fear, I would probably dump the stuff if the clearing time got to be 40 seconds...but that would be flying blind, also.