An update.(posted 8475 days ago)I was unaware of dead stop bath for a while (it's hard to see the indicator's dye color in slot processor - I'll switch to non-indicator stop bath and use pH indicator strip instead), and I noticed ammonia smell from my Ilford Multigrade fixer. I dipped in a pH indicator and it read about 7.5. This fixer has been used a little less than half of Ilford's published capacity.
If the ammonia smell of ammonium thiosulfate fixer is primarily depending on the pH value but not so on other factors then it is probably pH of 6 that one wants the fixer to maintain... but it would be nice if I could avoid sodium acetate... maybe lots of boric acid...