D23 precipitation

[ParkerSmithPhoto]

When I mix D23 (or Beutler's or BTTB), I always add the pinch of sulfite and then mix in the metol, dissolve it and then add the rest of the sulfite. It always looks perfectly clear when hot, but for some reason when it cools I always get a little sludge at the bottom. I’ve used it this way for years and never had any problems but I wonder if I’m doing it wrong.

 

[Alan Johnson]

The average calcium content in US tapwater seems to be about 30mg/L
https://www.ars.usda.gov/ARSUserFiles/80400525/Articles/NDBC32_WaterMin.pdf
However the solubility of calcium sulfite is only about 43mg/L
https://en.wikipedia.org/wiki/Calcium_sulfite
If the water is hard a precipitate of calcium sulfite may be produced.

 

[john_s]

I used to mix powdered Ilford fixer (Ilfofix) in Melbourne tap water (fairly low in dissolved substances I think) in a 1 gallon bottle (4.5L imperial gallon). When dissolved it was very slightly turbid (extremely slightly, just a bit short of crystal clear). After a few days there was a wispy deposit and the solution above it was crystal clear. I would decant clear fixer for film use so it would be as clean as possible. Some time later, I acquired a Fisons electric still and produced my own distilled water. When I used it for the Ilfofix, the slight turbidity never settled. Same general conditions (temperature etc).

I concluded that something in the Melbourne water was assisting in settling some impurities in the powder. Photographic grade chemicals are not ultra pure, and of course fixer wouldn't be critical anyway. I have not distilled my water even for developer stock solutions for 30 years and nothing has gone wrong.