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Tap Water

Question: Can I use Tap Water in my aquarium?

Answer: Yes, with a few simple precautions. Tap water is treated with chemicals, some of which incompatible with fish keeping. 

The two main culprits are Chlorine and Chloramines which are added to tap water as bactericides to reduce harmful bacteria and make it safer for humans to drink. Unfortunately, this makes it less suitable for use in the aquarium because both chlorine and chloramines are harmful to aquatic life.

Low levels can cause stress and irritate the gills,  higher levels around 0.2ppm can be fatal.  It can also have a detrimental effect on the bacteria in the filter system.  As bactericides they cannot distinguish between nuisance bacteria which can cause tummy up-sets in humans, and the beneficial strains growing in our filter systems.  As a result, undertaking a major water change with untreated tap water could decimate the filter and all fish life in the aquarium.

Chlorine is fairly easily removed, by agitation of the water, or simply leaving it to stand for 24 hours until the chlorine gas evaporates. It can also be neutralised immediately by the addition of any of the available de-chlorinators.

Chloramines are however much more persistent, indeed this is the very reason that they are now so widely used in the water supply industry.  Chloramines are compounds of chlorine and ammonia, and are more stable than chlorine alone. De-chlorinators, based on sodium thiosulphate, will neutralise the chlorine part, but release the ammonia into the water.  This can result in a dramatic peak in the ammonia levels before the filter can convert it to nitrite and on again to nitrate. Most modern de-chlorinators do cope with Chloramines but is is always worth checking.

As an added bonus, many good de-chlorinators will also bind to heavy metals which may be present in the water and render then harmless.

Maroon Clownfish in an Anemone