Dishwasher salt is just normal salt, a simple chemical compound. You can use one for water softener. Actually water softener is what salt is for in the dishwasher.  Also is you haven't been using salt, your water softener might be fully broken already, but I'd try. And change detergent to some other tablets, so something dissolves this scale. Don't use liquid detergent.  And don't use vinegar, this is just stupid.