Once mixed, stirring does nothing useful (except perhaps spread the heat around) unless it is a mix that contains organic matter that bacteria may consume, lowering O2. :)
I can’t speak to the salt as I never keep it around long enough, but I’ve found that keeping a small power head providing surface agitation/gas exchange with my RODI helps keep the “musty” smell away.
It could be a waste of power, but I’ve got a sensitive nose - not sure if it’s bacteria or what, but after a month or so in a brute the RODI smells a little cave-y.
