The Nitrogen Cycle

There are a few different names for what we call the nitrogen cycle -  biological cycle; nitrification process, or start-up cycle. Whatever you chose to call it, the process is essential to facilitate the growth of friendly bacteria in your fish tank, without which, the water can become toxic to your fish.


Allowing your tank to 'cycle' before you introduce new fish is essential to ensuring their long term health and wellbeing, and forms an important part of your fish care routine.

For this reason, understanding the nitrogen cycle - although it involves a little bit of science - can greatly improve your success of keeping fish.

The best way to monitor, and understand, the nitrogen cycle is to use an aquarium test kit that will test for ammonia, nitrites, nitrates and pH. Our OATA trained fish experts in-store are on hand to help you interpret your test results, so if you have any questions, please ask.


The Nitrogen Cycle

3 Stages of the Nitrogen Cycle

Stage 1: Decomposing plant, food and fish waste is added to you fish tank. The pH of the water in the tank will determine how this waste breaks down, and you will see a peak in ammonia levels.

Stage 2: Bacteria begins to develop, oxidizing the ammonia in the tank and removing it by changing it into what are known as nitrites. So, as your ammonia levels drop, the level of nitrites in your tank will rise.

Stage 3: The the nitrites  will be converted into less toxic nitrates. Nitrates are not as harmful to tropical fish as ammonia or nitrites, and once the nitrate level has stabilised in your tank it will be safe to add your fish.

Once your tank is established you will need to monitor the level of nitrates in the water as in large amounts, nitrates will be dangerous for your fish so maintaining a stable level is essential. The quickest way to rid your aquarium of nitrates is to perform partial water changes.

Controlling Nitrate Levels

Aside from partial water changes, there are a number of other ways in which the nitrate level in the water will be controlled.

  • In fresh water tanks, live plants will use up some of the nitrate to live
  • In salt water tanks, live rock and deep sandbeds offer large surface areas where baterica can break down nitrates and convert them into harmless nitrogen gas.  

Regular Water Testing

Carrying out regular water testing will help you monitor the nitrogen cycle in your tank. We can test your water for you and help you interpret results instore, but familiarising yourself with the testing process and using a home testing kit is recommended.

Peaks and falls in nitrate levels will happen as a result of changes in the population and levels of waste in the water.

Read Getting Started to find our how to start the Nitrogen Cycle in your fish tank.


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