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How To Test Fish Tank Water For Ammonia, Nitrites and Nitrates

Updated on October 1, 2010
Clear tests for, from left to right: ammonia, nitrite, nitrate and on the far right is a pH of around 7.6
Clear tests for, from left to right: ammonia, nitrite, nitrate and on the far right is a pH of around 7.6

Testing fish tank or aquarium water for ammonia, nitrites and nitrates is one of the most important things you can do for your fish, no matter what kind of fish you have. Why? Because these are chemicals which naturally build up in the water a fish lives in, and if they get too high, they can kill your fish.

Ammonia is produced when fish pee in the water. When your tank is cycled (when it has a living colony of bacteria which eat ammonia,) then your ammonia level should be pretty close to 0 the whole time. A new tank which has not cycled yet, but which has fish in it will build up large amounts of ammonia because there are no bacteria to eat the ammonia. If your tank has not cycled yet, and you have fish in it, you will need to keep an eye on ammonia levels by using a testing kit. If your ammonia rises above 0, perform 10 – 15% water changes daily until it is back down to 0. If your ammonia is high (above 0.25 mg/l), perform larger water changes, up to 25%, depending on how delicate your fish are. Fish such as bettas and goldfish can stand 50% changes as long as the pH does not vary too greatly.

Ammonia is highly toxic, not just to fish, but to humans as well. If we were exposed to 0.25 mg/L (ppm) of ammonia in our drinking water, we would get very sick too!

Nitrites are produced from the wastes of the ammonia eating bacteria. Nitrites are also poisonous to your fish, and should be monitored as well. Ensure that your nitrites do not rise above 0.3 ppm. If they are creeping up there, water changes are the key.

Nitrates are the end product of the ammonia / nitrite conversion process and are much less toxic than either ammonia or nitrite. However they still shouldn't be allowed to build up over time, which is why experienced fish keepers recommend a 25% water change every week. This also allows you to clean the gravel of any uneaten food or other debris and helps prevent cloudy water caused by bacterial blooms.

If you have a new tank, I highly recommend that you invest in a master test kit. This will test for pH, ammonia, nitrites and nitrates. There is nothing more devastating than losing fish, especially when you are new to the hobby, and you can easily prevent senseless deaths by keeping a close eye on the water quality, especially if you are cycling your tank with fish in it.

Cycling simply refers to building up colonies of good bacteria in the filter and on the surfaces in the tank. When your tank is cycled, the water quality will become much more stable, as long as the tank is not over stocked. If you know your tank is not cycled, then watch the water conditions, do plenty of water changes if you need to. (If you have a new tank, you should not have delicate fish in it anyway, so the fish you do have should be able to tolerate the water changes fairly well.)


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      Tamarind 8 years ago

      Very nice straight forward hub. This is important stuff that means the life or death of your fish and other aquatic life.