I have been using ABC+ PYRO from the Photographers' Formulary. Recently I had a bunch of my buddy's negatives to develop. They were FP4+ negatives.
I usually use HP5+ ( in a JOBO 2509 reel and tank, not the Expert Tanks). My negative density is fine when using HP5+. So when I tried my buddy's negatives, I found that the negatives were quite thin. I figure that maybe it waws the different film, and continued for a while til the negatives started getting thinner yet. So I mixed up some new developer ( yes, I know that the concentrate should last forever) and tried another bunch.. still thin negatives. Finally I ordered a new batch of TF4 fixer ( thinking my old fixer might be too old.)

Results.... I used my fresh developer, fresh fixer, eliminated the after fix Metaborate bath, and ended up with much more dense negatives. Mot quite as dense as I would prefer, but significantly more dense than the old chemistry was producing.

My conclusions.... my old fixer was somehow too old, and eating away at the emulsion somehow. Does any one have a similar experience, or can state some other reason for my results?