I've made up a solution of Sodium sulfite (anhydrous) at 30g/l ... it seemed fully dissolved and perfectly clear when I decanted from the mixing vessel to the storage bottle, but within a few hours a soft white precipitate formed at the bottom. I used water from an ordinary kitchen filter jug at room temperature. The sulfite was purchased from a reputable supplier of photographic chemicals.
I can easily run the solution through a filter it of course, but why should this have happened?
Would using Sodium hexametaphosphate (or similar) in the water, or deionised water, help avoid the formation of precipitate?