Sodium Thiosulfate Pentahydrate (Na₂S₂O₃·5H₂O) is a water-conditioning compound widely used in ponds and aquatic systems to neutralize chlorine and chloramine present in municipal or treated water supplies. These disinfectants can be harmful to fish, aquatic plants, and beneficial bacteria, and sodium thiosulfate pentahydrate safely converts them into non-toxic byproducts.

In pond applications, it is commonly used during water changes, new pond fills, emergency detoxification, or following chemical treatments. When applied at proper dosages, sodium thiosulfate pentahydrate acts rapidly, has minimal impact on pH, and is safe for fish, amphibians, invertebrates, aquatic plants, and biological filtration systems.

Because the pentahydrate form contains water molecules, dosing is calculated by weight to ensure effective dechlorination. Accurate measurement and thorough mixing are essential for maintaining a healthy and balanced pond environment.