Chlorine harms fish You DO NOT want it in YOUR pond!
Chlorine burns fish. It can damage their scales and gills and some severe circumstances it can kill.
Chlorine is added to drinking water in most parts of the world to kill bacteria. It therefore follows that if you fill or top up your pond you are adding chlorine to it and putting your fish at risk.
The equipment used to remove chlorine from water is called a dechlorinator. In simple terms a dechlorinator works by passing water through activated carbon and out into the pond providing chemically cleaner, chlorine free water.
The chlorine content in water varies from area to area and so there are no hard and fast rules as to how long the carbon will work before it is exhausted and needs to be changed, However, the life of the carbon can be prolonged by regularly back-flushing the unit (this should also be carried out before use the first time).
Water should be in contact with the carbon for approximately 4 minutes to enable it to absorb chlorine and any other impurities. If you know how fast you wish to fill your system you can work out what size dechlorinator to buy. Larger units contain more carbon and retain the water longer therefore enabling you to fill your pond faster.
The larger the unit the faster the fill.