The best replacement for sodium sulfite is sodium sulfate.

The best alternatives to sodium sulfite are rated as following:
★★★★★  sodium sulfate
★★★★  sodium bisulfite
★  sodium thiosulfate

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Speaking about sodium sulfite, one probably shouldn't forget about potassium permanganate.

Other search terms related to sodium sulfite and their ratings are:

★★★★★ potassium permanganate
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sodium sulfite
sodium sulfate
sodium bisulfite