Chlorine and Chloramine in the aquarium
Chlorine (and sometimes chloramine) are added to tap water to make it safe for humans to drink.
Unfortunately, this makes it less suitable for use in the aquarium because both chlorine
and chloramine are harmful to fish and other aquatic life. Lower levels could cause stress and irritate the gills of fish,
higher levels (around 0.2ppm) could be fatal.
Chlorine can be removed fairly easily in a number of ways. One method is to simply allow the water to
stand for about 24 hours (preferably with aeration) until it evaporates. There are also several brands of
commercial de-chlorinators available, based on sodium thiosulphate, which neutralise the chlorine. Some of these
water conditioners contain extra ingredients to bind toxic heavy metals or add a protective slime layer to the fish.
Chloramine is a more persistant chemical, and some water authorities use it because of its greater stability.
If you know or suspect that the water authority in your area uses chloramine, check that your dechlorinator
product removes it. Chloramine is a compound of chlorine and ammonia, which is more
stable than chlorine alone. Traditional dechlorinators, based on sodium thiosulphate, will neutralise the chlorine part,
but this releases the ammonia. With a large percentage water change, this could be dangerous or stressful for the fish,
as the bio-filtration will need time to convert the ammonia. The solution is a product which deals with the chlorine part
and also converts the ammonia into a non-toxic form.
Unlike chlorine, chloramine cannot be removed simply by aerating overnight. It is possible to remove chloramine in this way,
but it's likely to take several days of vigorous aeration with an airstone to remove it completely.
Filtration through activated carbon will also remove chlorine and chloramine - if this method is used it should be done in
a separate container for at least 24 hours, before the water is added to the tank.