Use a calcium/alkalinity supplement, and regular water changes should take care of everything else.
And above all, don't add anything if you're not testing for it. If you know your salt is low in magnesium, for example, add magnesium. But test before and after. Same for strontium, iodine, or anything else. The bottle doesn't know much about your tank, or how fast things are being consumed by your livestock. Also, beware of supplements that don't list ingredients and claim to do magical things.