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Sufficient chlorine is required to meet the chlorine demand (to disinfect the contaminants present) and to leave a 'residual' chlorine that will give protection from possible future contamination. Typically the target residual is 0.2-0.5 mg/l (as specified by WHO). It sounds like you are over dosing the chlorine. To determine how much chlorine you require you will need to analyse the water for the chlorine residual. A simple colour comparison kit with reagents are normally easy to buy in most countries.

If you provide more information about this particular situation we can give you more help.

Regards, Harriette