Tray life of TF-4 fixer?

I leave it in the tray and tick off the number of prints I fix on a sticky note on the wall, so I know when I've reached capacity. If you leave it for a long time, particularly in winter, the main concern will be evaporation. I've left it for a few months in a tray before replacing it (usually meaning I haven't done enough printing for a few months).

In my tankline I leave it for as long as a year, topping it off as needed.

 

Ansco 130 I put back in an Air-Evac bottle between uses. I was finding it was expiring after three days in a covered but not really airtight tray.

Porter's had a good deal on 2-litre Air-Evac bottles not too long ago. I don't know if they've sold out. They're much better than the old ones I have from the 1980s. With the old ones, air would seep in and they would expand over time. The folds of the newer ones kind of snap into place as you compress the bottle, so they don't expand.

 

I do the film strip test when I'm in doubt, and periodically check the pH of the fixer in my film tankline, but I think it's a pretty good bet that the manufacturer's recommendation for the capacity of TF-4 leaves a fair margin of safety. Have you found that not to be the case with TF-4, i.e, that the TF-4 has expired in your experience before fixing the equivalent of 30 8x10 FB prints per litre?