The best replacement for thiosulfate is sodium sulfite.

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

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Speaking about thiosulfate, one probably shouldn't forget about triiodide.

Other search terms related to thiosulfate and their ratings are:
★★★★★ triiodide
★★★★★ iodine
★★★ iodate
★★★ kio3
★★ chlorine
★★ hypochlorite
★★ nitroprusside
★ potassium iodate
★ iodine reaction
You have in mind a companion for thiosulfate and it is not yet here? Propose!



Google Trends

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thiosulfate
sodium sulfite
ammonium sulfate