Chlorine and Chloramine
Chlorine or Chloramine is added to most domestic water supplies. They kill the bacteria and other germs. Unfortunately they are also poisonous to fish. The effect on fish is very rapid and the Chlorine or Chloramine should by removed before the water comes into contact with fish. Turtles are more resistant to Chlorine and Chloramine, but some deaths have been reported from Chloramine poisoning.
In the some areas Chlorine is added. This can be removed by adding the recommended rate of any of the Chlorine removers sold in aquarium shops. Another way of removing it is to allow the water to stand for 24 hours in an open container. Some domestic water filters will remove Chlorine and Chloramine.
In some places it is illegal to add Chloramine to domestic water supplies.
In the Adelaide Hills most of the areas have Chloramine added, despite the health problems apparently caused by it in some people. (The cause and effect relationship has not been proved.)
Chloramine is a combination of Chlorine and Ammonia. This is much more stable than chlorine alone and is much more poisonous to fish. To get rid of it by allowing the water to stand in a wide topped open container, if the water is clean, would require at least 3 weeks.
The more common way of removing it is to add a Chlorine remover. The rate needs to be 5 times the recommended rate. Not all Chlorine removers are safe at this rate. Wardley "Tristart", Aquarium Pharmaceuticals "Super Strength Tap Water Conditioner" and CPV "Complete Water Treatment' are all safe at the concentration required.
These products at 5 times the normal rate will all remove the Chlorine, but not all detoxify the Ammonia as well. With the others, if the pH is lowered to below 7.2, the Ammonia from the Chloramine should be below the dangerous level.
An established tank should not normally need to be completely emptied. Normally a partial change using a gravel washer will be sufficient. This will reduce problems caused by water changes.