Interesting topic!……
I do have some citric acid…….the remains of a small pack that came from Cup-Alloys and a larger bag from a brewing supplies outlet. It's not expensive, is safe for humans and is easy enough to use…..
However, I have stopped using it now as I did'nt really like how it treated my clock parts. Citric quickly turns brass parts a distinct pink colour, presumably by removeing the surface zinc so that copper is uncovered and also b y giving the surface finish a 'satin' or semi-matt effect. All these symptoms show up quite quickly.
I now just wash and lightly scrub brass parts in ordinary household detergent in hot water and use a soft nylon nail brush. So far I have not seen any problems with flux etc being retained around joints and will go on using it instead of citric….although there may well be a chance of using the unique look of citric on a future clock.