Sea salt and Witchcraft.?

Yes, it's perfectly okay to reuse salt. If you start noticing a change in the feeling of items removed from the salt, you may want to dispose of it (respectfully!) and then start with a fresh batch. Sea salt will always have a certain amount of iodine, since it is naturally occurring in sea water. The sea salt that is marked as having iodine has extra iodine added to prevent people from developing goiter from a deficiency of iodine. It make no difference for magical workings what kind of salt you use - sea salt, rock salt, kosher salt, even the kind you buy for the salt shaker!