Response to Stopbath - further to below

I have never used an acid stop for film, preferring an intermediate wash. However, pinholes sound very much like the bath was improperly used. They are presumably caused by the acid reacting with developer alkali (such as soda), liberating gas (CO2). If this happens at a rate too fast to allow diffusion of the gas out of the emulsion, small bubbles may result, which then look like pinholes. Correctly mixed stop is indeed not much more than coloured water, its concentration typically being 5% or even less. Consider that you don't want to positively acidify the film but to neutralise the alkali in the emulsion. Not much acid is needed to accomplish this.

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