This bit of info is new to me: "AFAIK, no Kodak or Ilford film or paper needs a hardening fix, all of which are acid and use alum, or which are alkaline and contain formalin and no Ammonia. Recent reports say that some Fuji films may need a hardener. Many European films benefit from a hardening fix. The only way to know for sure is trial and error."
I've stopped using Tri-X sheet film since they changed some years ago, found it disappointing. Prior to that, I started using hardener after I got reticulation when my wash temp fluctuated. It didn't fluctuate that much, from cold to warmish, not hot, but it reticulated severely. I'm using T-Max - 400 now, with hardener. I wonder if I still need it? This is a great thread, BTW.