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Water is the fishes atmosphere and serious consideration must be given to its supply and condition. The fish we keep in our aquarium can come from several different types of water depending on its origin. It is not too difficult to maintain a successful aquarium with a collection of fish from different continents. However some fish are fussier in their requirements and may die if given the wrong water conditions. If you plan to breed your fish then a much deeper knowledge of chemistry is needed. There are still many fish that have not been bred in captivity; this is due to us humans not being able to mimic the water conditions of their natural environment.

Chlorine and Chloramine are added to water to eliminate harmful bacteria in drinking water for human consumption, but are very toxic to fish, beneficial bacteria and plants. When first setting up an aquarium and whenever partial water changes are conducted, always use water conditioner to make the tap water safe for fish.

It is important to ensure that you maintain the correct water conditions for you fish. This can be monitored weekly by use readily available water testing kits. Most water chemistry can be altered by the vast array of products available today.

Water Treatment

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Reverse Osmosis

Reverse Osmosis filtering of water is done by forcing the water under high pressure through a porous membrane. The holes in the membrane are large enough for the water to get through but trap larger particles which would be impurities . The "high pressure" part is the key as the holes in the membrane are so small that nothing would get through without it.Click here for information on specific products.

Acidity / Alkalinity

Acidity and alkalinity are measured on a scale of 1 (very acid) to 14 (very alkaline). Both extremes are lethal to fish and plants, especially if you bear in mind that water having an acidity of 6 if tem times as acid as water with an value of 7. Acidity/alkalinity is represented by the symbol pH, with pH7 indicating neutral conditions. All values below pH7 are increasing levels of acidity, while those above are increasing levels of alkalinity. Most freshwater fish prefer pH values between 6 and 7.5.

pH Test Kit


Hardness is also important when creating a ‘natural’ environment for your fish. Hardness is due to dissolved salts from calcium and magnesium. There are 2 types of hardness general (GH) and temporary (KH). When temporary hardness is low, water loses much of its buffering capacity and can lead to rapid fluctuations in quality. This can be removed by boiling your water. General hardness is important in a different way. Fish that originate in soft water e.g. the Amazon need low GH, while fish from African Rift lakes need a higher GH. Hardness Test Kit


Ammonia is released by most living organisms as part of the break down of organic matter. Fish waste contains a high level of ammonia. Ammonia is very damaging to fish health, it irritates the gill and skin surfaces, destroys the protective mucous coating of the fish. Even at levels below 0.01 ppm ammonia has been shown to lower the immune system of fish.


Ammonia Test Kit

Nitrites / Nitrates

During the natural biological purification, ammonia is converted into nitrites that are also toxic to fish. Nitrites must be closely monitored in new tanks set-ups. However with a good population on filter bacteria these nitrites are converted to nitrates, whose concentration needs to rise above 50mg before becoming toxic to delicate fish species. Nitrates can be kept at a minimum by regular water changes.


Nitrite Test Kit