Quick Definition:

Sodium thiosulfate is a common reagent chemical found in swimming pool test kits, often used to test the pH level of pool water.

What is Sodium Thiosulfate in swimming pools?

Sodium thiosulfate, also denoted as sodium thiosulphate, is a colorless crystalline compound.  It is commonly known as an antidote to cyanide poisoning, used as an additive to bleach, and as a chemical used to test the pH of bleach products.

For swimming pools, sodium thiosulfate is used as a reagent in the testing of pool water, primarily to neutralize the whitening effect of chlorine present in a water sample.  High levels of chlorine can alter the expected color indication for water balance test such as pH, and sodium thiosulfate is first added to the sample to ensure a valid test result.

Sodium thiosulfate can also be used in larger quantities to treat chlorinated waste water from pools before disposal to the surrounding environment, and can be used to reduce chlorine levels in swimming pools.

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