• Chlorine neutralizer for swimming pool water
• Single-ingredient product: sodium thiosulfate pentahydrate, 100% w/w
• Colourless, odourless crystals
• Not classified as hazardous under GHS, but still an irritant — see the safety notes below

Safety, handling and storage (from the Regal CHLOR OUT Canadian Safety Data Sheet, issued 5 June 2024)

• Not classified under GHS. The SDS still notes: “May irritate skin and respiratory tract. May irritate and/or burn the eyes. Reacts with acids to form toxic and irritating sulfur dioxide gas and/or hydrogen sulfide gas.”
• Avoid contact with skin, eyes and clothing. Do not breathe dust or mist; use adequate ventilation. Wash thoroughly after handling.
• The SDS notes: “If dissolving and mixing solutions with the pentahydrate material (crystal), the reaction is endothermic and the solution will cool.”
• Storage: “Store in a cool, dry, well-ventilated area away from acids and oxidizing agents. Keep container closed when not in use and protect from physical damage.”
• Incompatible materials: “Strong oxidizers cause vigorous exothermic reactions. Acids release sulfur dioxide and/or hydrogen sulfide gas.” Never mix this product with chlorine products, acids or any other pool chemical.