a bit of vinegar might tell part of the story, but the precipitation I have seen is not very substantial however. (At least not enough to merit throwing out the batch of salt)
If there is substantial residue, perhaps pitching it out is appropriate but so far, I have only seen small amounts this happens with.
Johanthan,
Now suppose this.... if it is calcium carbonate, could you not put it back into suspension with a bit of vinegar?
I say this because in some cases where a tank needs a bit of a CA boost, we will add vinegar to our Kalk solutions to lower the PH and so allow more dosing.
I realize this is a different principal (lowering PH vs dissolving CA) but doesn't the CA re-enter the water column all the same? I do not know what the chemical process does to the CA