Key Concepts: The Nitrogen Cycle

The Nitrogen Cycle - An Illustration

Now the Nitrogen Cycle is something EVERY aquarist (fish keeper) should know. Even those who don’t know or understand it know they should know it. Although within your fish tank the Nitrogen Cycle works on a very small scale, it is undoubtedly one of the most important chemical processes that happen within your tank and dictates everything from your tank maintenance schedule to how often you perform water changes, and much more in between.

What is Nitrogen, and what role does is play?

Nitrogen in itself is an unreactive gas that makes up around 78% of Earth’s’ atmosphere. It’s essential in life because it enables the formation of amino acids in proteins.

Nitrogen within the fish tank…and the Nitrogen Cycle itself:

The ‘Nitrogen Cycle’ is the term used to describe the conversion of ammonia (very toxic) from fish waste, decomposing plant material, and left over foods into Nitrites (toxic), and then into Nitrates (not so toxic).

Here’s a great illustration of the Cycle


The Nitrogen Cycle - An Illustration

The Nitrogen Cycle – An Illustration (click for full size)

A great video about the Nitrogen Cycle:

Credit: MyFishCare101


  1. bennygayle

    When I first began keeping goldfish, I happened upon an article about the nitrogen cycle, and thought; I don’t need to know this stuff, this is for biologists. I was so wrong. Every fish keeper must learn and get to know all about nitrogen cycle. The lives of your fish depend on it

    Something missing in this article, Key concepts, is algae. I believe algae is a part of the nitrogen cycle. It completes the circle of aqua life

    Ammonia is created from waste. When ammonia is present, beneficial bacteria form to feed on it. The convert it to nitrites. When nitrites is present, another type of friendly bug forms to feed on the nitrites, converting it into nitrates, what the experts refer to as the end result of the cycle, which isn’t true

    When nitrates is present, algae forms to feed on the nitrates. Just like the beneficial bacteria, algae is made up of living micro-organisms, and is a food source rich in vitamins and minerals

    The fish eat the algae, and make waste, and so the production of ammonia begins

    Learn everything you can about the fish you keep, and don’t consider algae as grunge in your aquarium, but the amazing life form that it is

    1. FishFanOne (Post author)

      Although many people have disagreed with algae being beneficial in your fish tank, I personally allow it to grow in my tank Benny, for a number of reasons:

      1. As you’ve already mentioned – it’s a fantastic source of nutrients for your fish. Both fish and invertebrates feed on the algae, and it’s good for them.

      2. It helps soak up excess nitrates and acts partly as a control mechanism for the overall water quality in the tank.

      3. It can be used as an indicator of water quality also. Many aquarists conduct water changes weekly and are completely anal about test results. Some, unfortunately aren’t so good at looking after their tank.
      An explosion in algae growth (also known as an ‘algae bloom’) is a great indicator of a spike in nitrates and your water should be tested immediately. So yes, allowing algae to grow in your tank can be used as a great visual indicator to the quality of your water.

      Personally, I allow algae to grow on the back wall of my tank to allow for readily available nibbles for my tank inhabitants, and I only rarely clean the side panes of my tank. The only glass I keep completely free of algae is the front pane – or the ‘viewing’ pane.


  2. brenda rand

    Let’s say most people disagree that algae is beneficial, and these are the people that don’t know or understand what algae is. It’s often mistaken for grunge and thought to be related to fungus or bad bacteria

    Completely understand your wanting to remove the algae from the front and sides of the glass to keep from obscuring the view. I keep my fish in a stock tank, so that’s not a problem

    1. FishFanOne (Post author)

      Would love to see some pictures Brenda :) Please, share some with our community of Bluewavers :)



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