Potassium Metabisulphite is sold in Home Brew shops and Boots The Chemist (UK) used to stock it. in 250gm Bottles.
Now back to Rodinal :D
What I was trying to suggest or rather asking is the effects of "the one SO2 and one mole of SO3 upon decomposition in water, both of which end up making HSO3- or the equivalent. It is acidic in water."
I'm referring to the "Orginal formula" Andresen suggests, and many book from Agfa in the early 1900's right through to the recent Darkroom Cookbook.
Yes it's definitely acid until the formulae is balanced with Hydroxide, my point is something different is happening when Metabisulpite's used because of the SO2 & SO3 which won't happen if we used the equivalent amount of Sulphite.
In most developers using small amounts of Metabisulphite it's probably irrelevant but in this old developer with such a high level it has to make a difference.