It seems I am having trouble mxing up sulphite from metabisulphite. (I can only buy sodium sulphite here and from pool shops not from the photo chemical suppliers who only have metabisulphite.. and I want the potassium salt, edit: Vanbar has sodium sulphite now) I am following: K2SO5 + 2KOH = 2K2SO3 + H2O When I mix it I usually get undissolved matter remaining, requiring filtration, is this because of the heat produced from the reaction by the KOH? What is the best method of production? Metabisulphite in water, KOH in water, add KOH solution to metabisulphite? Add metabisulphite solution to KOH? Metabisulphite powder to KOH solution? KOH flakes to metabisulphite solution? I also remember reading somewhere that heat will 'wreck' the sulphite, so am not able to boil off the remaining water to collect dry sulphite?