Difference between Sodium Metabisulfite and Sodium Bisulfite? SMBS is commonly used for removal of free chlorine and as a biostatic. Other chemical reducing agents exist (e.g., sulfur dioxide), but they are not as cost-effective as SMBS. When dissolved in water, sodium bisulfite (SBS) is formed from SMBS:
Na2S2O5 (sodium metabisulfite) + H2O –> [....]