Some people go up to year on Supplements - Vitamins.
I try not to go past 6 months...just to be safe.
I think some Calciums are a little more safe on the "shelf" / closer to a year, but vitamins definitely aren't IMO.
We usually go through a container of vitamins between 6-8 months.
We use the Rep-Cal calcium. It is my understanding that the calcium does not breakdown since it is a mineral (think rock).
I always find that I can never go through all the supplements in any given container before the 6 month window passes.
For that reason, I always use a pinch more than I actually need and just dump it into the viv with the flies. The first time I did this, it was totally by accident. But the next day, when I saw the SWARM of springs, isos AND FF's all over the little pile of supplements, I decided to start doing it every feeding. It's a little feeding station without wasting perfectly good fruit/veg.
Yep....I never throw away my "old" or expired vits and calcs. I dump them into my huge FF media storage barrel. Better than just throwing them in the trash.
Jim pointed this use of old supplements out....use your 'old' / expired supps in the dusting cup to knock off any mites that are hitchhiking on your FF when you go to make new cultures.
The superfine powder combined with the swirling and shaking causes the mites to come loose and not be able to get a grip or traction due to the slick powder. Powder will also quickly dessicate (dry out) mites.
Ever wonder if your cx's may have some mites but ya can't really see em ? Just swirl your flies really well and vigorously in the powder, which you should be doing anyway, then feed out all the flies but make sure a decent amount of excess powder remains in the dusting cup.
Let the dusting cup sit for several hours to 1/2 a day and then observe.
If you had/have a noticeable mite infestation, you will see this by looking at the dusting cup. The mites will sometimes cling together in little brown, dusty groups - looking a little fluffy.