I never re-use fix - either for film or for prints. (For prints I currently tend to use one bath of Hypam at 1 : 4 (and throw) - if I was using a 2-bath fixer I would keep it for the second bath). The test for fixer freshness from the bottle is still useful - but I don't think I ever keep it long enough for it to go off (I buy the 5l bottles).