The Easy Guide to the Nitrogen Cycle For Aquariums

The Easy Guide to the Nitrogen Cycle for Aquariums

Are you getting started with your first fish tank? Then you may have heard of something called the “aquarium nitrogen cycle,” followed by a bunch of complicated scientific terms and graphs that seem a little overwhelming. Do not panic! Keep reading as we explain the nitrogen cycle in this very short and simple guide.


What is the Nitrogen Cycle for Aquariums.

The nitrogen cycle basically describes how nature creates food (in the form of microorganisms and plants), fish eat the food and produce waste, and then nature breaks down the fish waste so that it can get converted into food again.

An illustration of the nitrogen cycle for aquariums.

Aquarium hobbyists refer to the part where fish waste converts into toxic nitrogen compounds like ammonia or nitrites. If we don’t have enough microorganisms (also called beneficial bacteria) to eat the waste products, these nitrogen compounds could potentially cause death in our fish.

To illustrate the three toxic compounds, we will use M&M’s yellow, brown and blue M&M’s.

Yellow = ammonia, which is extremely toxic and can cause serious skin irritations in fish.

First Step: Some ammonia will be produced when your fish goes to the toilet.

Step 2 Beneficial bacteria #1 consumes ammonia and makes nitrites.

Step 3: Beneficial bacteria #2 then eats the nitrites and produces nitrates (the least toxic nitrogen compound).


4. The fish continue consuming food and produce waste. These are converted from ammonia to nitrites and then into more nitrates.

Step 5 Over time, nitrates build up and can cause fish to become sick. You can remove nitrates by changing the water or using aquarium plants. (Aquarium plants can use the nitrates in order to produce new leaves.

“Cycling your aquarium” simply refers to the process of making sure you have enough biological filtration (e.g., beneficial bacteria and aquarium plants) so that all the ammonia and nitrites get eaten up right away. If you have multi-test strips or ammonia tests, you should aim to get 0ppm ammonia, 0.ppm nitrites, as well as some nitrates. You should remove any tank water that has nitrates above 40 ppm and then replace it with clean, fresh water.

How long does it take for an aquarium’s cycle to complete?

It all depends on how long it takes, but typically it takes anywhere from a few months to a few months. This can be accelerated by purchasing a bottle of live bacteria, obtaining used filter media from someone you know, or even growing live plants, which also have beneficial bacteria. You can read the complete article about how to cycle an aquarium.

Most hobbyists will answer yes or no to the question of whether their aquarium is cycled. However, the truth is a bit more complicated. The question should be “How many beneficial bacteria is the tank able to support the fish waste treatment?”

How Do I Increase My Biological Filtration?

This naturally leads us to ask how to we make sure there’s enough biological filtration in the aquarium to handle toxic nitrogen compounds. The easiest way to do this is to add more aquarium plant, which will happily eat the ammonia- and nitrates that your fish waste produces. Just remember that if you don’t have enough fish waste to feed your plants, they could starve to death, so you’ll need to supplement with a good, all-in-one fertilizer like Easy Green.

There is a common myth that larger or more filters will result in more beneficial bacteria. It is not true that beneficial bacteria can grow in aquarium filters alone. They also thrive on the gravel, glass walls, and decorations. You will have more beneficial bacteria if you buy more filters. But if you only have one fish, then your decorations may be enough to sustain the beneficial bacteria.

To find out how often you need to do water changes on your aquarium, download our free infographic that guides you step-by-step through the process.