Answer
Dissolve 1 teaspoon of granules in 7–8 litres of water to make a stock solution; add 1 part of this to 100 parts of the water to be treated, mix and let stand 20–30 minutes before use. For a tank, roughly 1 lb (450 g) per 10,000 gallons gives about 5 ppm.
Detailed question
How do I disinfect water with chlorine powder?
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