i completely agree rock salt that is black salt and sendha namak can be used as a substitute.According to me low sodium salt should not be used much as its too high in potassium,so may have adverse affects on the heart and kidney.The key is to have salt in moderation.The allowance is 5 gm of table salt per day.1 tsp or 5 gm of table salt contains 2400 mg of sodium.