Stoo suggested a one time use on film processing then, the fixer is re-used till exhaustion (or your preferred usage level) in your printing session.
And as Stoo referred to the silver particules. I don't know if it is what I saw yesterday (I suspect it is). I saw tiny particules, here and there, at the surface of one of my films drying yesterday. (Definitely not dust). They were visible only when the film was wet (can't see anything now nor water mark). I don't know if that was silver particules.
With that in the back on my mind, I tested the fix this afternoon, I gasped.