Unlike most other pets, fish are 100% dependent upon their keeper for the quality of their environment. Pretty much all fish keeping environments start from the same place-tap water. The key thing to remember is that tap water is produced to be healthy for humans to drink, end of story. No attention is paid to the needs of fish or other pets in its production and arguably none should be.
To prevent diseases tap water is treated with a disinfectant (normally chlorine or chloramine) which is good news for us but very bad news for our fishes. Chlorine is acutely toxic to fish and can kill within minutes by causing severe gill damage and subsequent asphyxia. Thankfully, chlorine dissolves in water to produce hypochlorite (Cl2O2) ions which are unstable and are consequently very easy to remove. Simply bubbling air through the water or leaving it to stand for a few hours will drive off the chlorine. Alternatively aquarium tap water conditioners can be used to instantly detoxify the chlorine. These are generally based on Sodium Thiosulphate (Na2S2O3) which reacts with the chlorine to produce harmless chlorides and sulphates. Chlorine can also be removed by filtration over activated carbon.
Unfortunately, the instability of chlorine in water has encouraged utility companies to look for a "better" disinfectant that will stay in the water for longer. One such disinfectant is chloramine, a combination of chlorine and ammonia. From a fish keeping point of view chloramines can be far more dangerous than chlorine because they don't simply "go away". Toxic chloramine levels may persist for a week or more in water left standing in a bucket! Even bubbling air through tap water treated with chloramine will have very little effect. Worse still treating the water with a traditional (sodium thiosulphate) based dechlorinator will split the chloramine back down into chlorine and ammonia. The chlorine part will be dealt with but the ammonia will remain in the tank potentially killing the fish. If you suspect that your tap water contains chloramine it is vital that you choose a tap water conditioner specifically aimed at treating it. These normally combine a dechlorinator function with an "ammonia locker", such as sodium hydroxymethanesulfonate.
It isn't all bad news though. Chlorine kills fish by burning their gills, once this damage is done death is fairly certain and there is little that a fish keeper can do to help. Chloramines on the other hand cross the gills without causing physical damage and enter the bloodstream. Once in the blood stream they bind to haemoglobin and prevent it from carrying oxygen properly. This condition is called methemoglobinemia, affected fish appear sluggish and often gasp at the surface trying to take in more oxygen. Thankfully,it can often be reversed by removing the fish to chloramine free water and treating them with methylene blue. Methylene blue rapidly converts non-oxygen carrying methemoglobin back into oxygen carrying haemoglobin and the fish often make a full recovery.
Having to take a little more care in preparing our fish keeping water is a small price to pay in comparison to the numerous human deaths that chlorination and chloramination prevent. At the end of the day far more people drink tap water than keep fish in it!
© 2006 Dr Andrew Whiston. All Rights Reserved. This document may be freely redistributed in its unedited form and on the condition that all copyright references are kept intact along with the hyperlinked URLs.
Dr Andrew Whiston is a professional biologist with over 30 years fish keeping experience in Retail and Public Aquaria. Found on the web at http://www.standrewsaquarium.co.uk
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