Sanitizer - use 2 oz. per 1 gallon of water. Antioxidant and bactericide - use 1/4 teaspoon to 6 gallons. Dissolve sulphite in warm water before adding. Sodium metabisulfite or sodium pyrosulfite is an inorganic compound of chemical formula Na2S2O5. The substance is sometimes referred to as disodium metabisulfite. It is used as a disinfectant, antioxidant and preservative agent. Sodium Metabisulfite is not recommended for those with asthma. Inhaling the fumes could possibly induce an asthma attack. Potassium Metabisulfite is recommended in its place, if you need a substitute.