The pH per se is not reason why a fixer does or does not bleach the developed silver. As for staining developers, the conventional wisdom was that acidic solutions inhibit the formation of, or reduce the amount of stain. However I have still not seen proper tests that conclude either way. First there is the question as to whether the pH of the stop bath, fixer and wash water influence the degree of stain. Second, one must differentiate between the effects (if any) on general stain and imagewise stain. Third, it apparently depends on the developer formulation itself. For example Hutchings always said an acidic fixer and acidic wash water would reduce/inhibit stain with PMK (whether it is general or imagewise stain is a murky issue). Yet he does recommend an acidic stop bath. Some rigorous testing is definitely needed here. On the other hand, John Wimberley claims the full imagewise stain with WD2D/WD2H is formed in development and is stable thereafter, meaning you can use an acetic stop bath and aa regular acidic rapid fixer with no problem. He has done a fair bit of testing on this.
Originally Posted by Steve Smith