Sodium thiosulfate is the cheapest + fastest dechlorinator. How it works: reacts with hypochlorite to form sulfate + chloride - both harmless. Reaction completes in seconds. Found in: Seachem Prime (combined with sulfite + ammonium chelator), API Stress Coat (with aloe vera), Tetra AquaSafe, ClorAm-X, plain pool dechlorinator (cheapest at $5/lb). Pure form (DIY): 1 teaspoon per 50 gallons neutralizes municipal chlorine. Buy as "pool dechlorinator" or photographic-grade thiosulfate. Limitation: does NOT detoxify ammonia. Chloramine breaks into chloride + ammonia; thiosulfate handles the chloride but leaves the ammonia. Need a separate ammonia detoxifier (Prime's sulfite or alpha-keto detoxifiers like ClorAm-X) for full chloramine treatment. Caveat: overdosing depresses dissolved oxygen briefly - don't triple-dose.
Reviewed by the Fast Aquatics husbandry team · Updated May 2026
Full glossary · Q&A library · Calculators · Disease database · Care guides