Response to Stopbath - further to below

AFAIK, Citric acid is the base for most of the odourless fixers. I wouldn't recommend hydrochloric acid, as it's too strong. This means that slight overdoses may be fatal. Besides, it's much more difficult to handle and much more dangerous than citric acid. If I recall this correctly from my chemistry lessons, there is even another problem with strong acids: Strong acids tend to give a step-like change in pH. The pH of the stop - and therefore that of the treated film - is either very acid (if there was a little too much acid) or very alkaline (if there was too little). (It's a bit like with graphical films: They are either black or white, but never gray.) Weak acids, otoh, have a smoother titration curve. This means that a little too much alkali or a little too much acid doesn't make so dramatic a difference in pH.

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