What is the Nitrogen Cycle?

We’ve all heard of the carbon cycle in school right? But what about the Nitrogen Cycle? Is this even a thing?  How important is it really in the establishment of good aquariums and ponds? Is there a difference between aquarium nitrogen cycles and pond nitrogen cycles? Today we’ll find out. 

If you want to create a sustainable and long lasting aquarium or pond with little to no maintenance, the proper understanding of the Nitrogen Cycle is essential for your success. This is especially so in the case of a stagnant pond in a pot type of setups where nitrogen-containing waste can pile up and accumulate to extremely toxic levels. 

The Nitrogen Cycle is  one of the most critical yet highly misunderstood concepts in the hobby of fish-keeping. The Nitrogen Cycle is of utmost importance for maintaining a sustainable and healthy aquarium or pond. Despite this, there are numerous hobbyist who fall victim to algae blooms, dead fish and other types of disasters due to their lack of understanding of the Nitrogen Cycle. 

A typical aquarium setup and the organism which contribute to the Nitrogen Cycle.

What makes up the Nitrogen Cycle?

So what are the components of the Nitrogen Cycle? To sum it up nicely, there are 3 components in the cycle.

Ammonia /Ammonium (NH3/NH4)

Live animals such as fish, shrimp and snails all produce waste matter which contains a high amount of toxic ammonia. Additionally, uneaten fish food will also eventually be broken down to produce even more ammonia in the waters. Furthermore, ammonia is also produced as bacteria and other decomposers break down organic waste matter within the pond or aquarium. This form of nitrogen is extremely toxic to all types of fish even at low levels, and can pose a significant threat to their health.

Nitrite (NO2)

Beneficial bacteria in the waters known as Nitrosomonas Bacteria will break down the harmful and toxic ammonia into Nitrite, NO2. It is still harmful to your fish, however much safer than NH3. However, it will still be toxic if levels get high enough. This form of nitrogen is an intermediary and will eventually have to be converted as well in order to not pose a threat to the fishes and other live animals in the waters.

Nitrate (NO3)

Another group of bacteria known as the Nitrobacter will break down and convert the Nitrites into Nitrates, NO3. The Nitrate is then used and assimilated by plant life in the pond or aquarium as a source of nourishment and “fertilizer”. Nitrates can only be removed by live plants or water changes. For instance, the water lily is a very nitrate hungry plant and removes large amounts of nitrates from ponds to be used as nutrients. Bacteria are no longer able to remove this type of nitrogen compounds from the waters. These are also the compounds responsible for algae blooms if present in large amounts.

What does all this mean for my plants and fishes?

From this information, we hope you are able to witness how each phase is dependent on the one that came before it to survive. Because of this, it takes time to properly establish all the bacteria colonies to fully complete the nitrogen cycle.

The right amount and quantities of fish, plants, Nitrobacter and Nitrosomonas are required to create a well-balanced and healthy nitrogen cycle which translates to a healthy ecosystem. A healthy ecosystem will basically translate into less maintenance for your aquarium/pond and happy healthier plants and fishes.

A quick summary of the Nitrogen Cycle
Nitrogen Cycle Diagram
A simplified example of the Nitrogen Cycle in Aquariums and Ponds

But how do you then ensure the right amount and quantities of each entity within your waters?


No, not peddling the damn bicycle. I mean cycling the tank, or in some cases, the pond. Cycling is a process which introduces the right amount of beneficial bacteria prior to adding fishes into the media, stabilizing the amounts of bacteria (Nitrobacters and Nitrosomonas). This ensures that there will not be a sudden surge in ammonia when fishes have to go to the toilet to take a poo. Proper cycling ensures that there will be sufficient bacteria to process and convert the toxic ammonia into other forms of nitrogen such as nitrites and nitrates. 

The correct understanding and application of the nitrogen cycle will help to create a better ecosystem for both your plants and animals within the pond or aquarium.

Stay happy, First Floor Family.

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