Precipitate in Sulfte solution

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?

If you used tap water then the white precipitate is probably calcium sulfite. Next time use distilled or de-ionized water.

Thank you Gerald