Sodium sulfite and sodium thiosulfate are two of the most common chemicals used to dechlorinate pool water. Although they are somewhat similar, and sodium sulfite is used in the production of sodium thiosulfate, they do have differences. Many municipalities require dechlorination before disposing of pool water, so you will need to be familiar with these differences to make the right choice for your own at-home pool maintenance.
Manufacturers sell sodium sulfite in tablet form, while sodium thiosulfate comes in a powder. Many people who routinely perform pool maintenance find the tablets easier to store, to handle and to use.
Environmental protection advocates consider sodium thiosulfate to be less hazardous to the environment and marine life than sodium sulfite, because it is less of an oxygen scavenger. This is important, because when you dispose of your pool water, it eventually makes its way back into rivers and oceans.
Sodium sulfite is less costly than sodium thiosulfate. It costs less initially. In addition, it dechlorinates more effectively than sodium thiosulfate, meaning that you need to use less of it to treat your pool water.
Sodium sulfite is relatively unstable. If it is not stored properly, it will break down and no longer be effective. Sodium thiosulfate is more stable, meaning that it is preferable if you need to store your pool chemicals over time rather than using them immediately upon purchase.