Kent Mg precipitate

[scyphozoa]

I have an old (maybe 3 more years) bottle of Kent Tech M additive which I got out today and was trying to decide whether it was still usable. Looking in the bottle I noticed a gray/tan precipitate on the bottom. What could this precipitate be and is it usable or do Mg additives expire?

[Randy Holmes-Farley]

It won't expire. I'd still use it, but leave the unknown solids behind as much as you can. :)