The Easy Guide to the Nitrogen Cycle for Aquariums

Are you getting started with your first fish tank? You may have also heard of the “aquarium Nitro cycle,” which is a series of complex scientific terms and graphs that can seem overwhelming. Don’t panic! We will explain the nitrogen cycle in this short guide.

What is the Nitrogen Cycle in 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.

Here is a simplified diagram showing the nitrogen cycle in aquariums

When aquarium hobbyists talk about the nitrogen cycle, they are usually referring to the specific part of the cycle where the fish waste turns into toxic nitrogen compounds like ammonia, nitrites, and nitrates. These nitrogen compounds can potentially kill our fish unless we make sure we have plenty of microorganisms (also known as beneficial bacteria) and plants to consume the waste products.

For the purposes of our illustration, let’s use yellow, brown, and blue M&M’s to represent the three toxic nitrogen compounds:

– Yellow = ammonia (which is very toxic and can burn fish gills and skin) – Brown = nitrite (which is somewhat toxic) – Blue = nitrate (which is not as toxic as ammonia and nitrite)

Step 1: Whenever your fish goes to the bathroom, some ammonia is produced.

Second Step: Beneficial Bacteria #1 eats ammonia, and produces nitrites.

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

Step 4: The fish continue to eat food and produce waste, which gets processed from ammonia and nitrites into more nitrates.

Step 5: Eventually, the amount of nitrates will build up and can become harmful to the fish in high amounts. You can remove nitrates by changing the water or using aquarium plants. (The aquarium plants consume the nitrates to produce new leaves.)

Cycling an aquarium is simply the act of making sure that your tank has enough biological filtration, such as beneficial bacteria and aquarium plants, to ensure that any ammonia or nitrites are eliminated quickly. Multi-test strips or ammonia test strips should be used to measure the ammonia and nitrite levels in your tank water. If the nitrates reach 40 ppm or more, then you need to remove some of the dirty tank water and replace it with fresh, clean water.

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

It depends, but usually it can take anywhere from a few weeks to 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. For more details, read the full article on how to cycle your aquarium.

Most hobbyists will answer yes or no to the question of whether their aquarium is cycled. The truth is that the answer to this question is more complicated than it seems. Instead, we should be asking, “How much beneficial bacteria does the tank have, and is it enough to treat the waste produced by the fish?” For example, if you have a “cycled” aquarium with 3 neon tetras and then suddenly you add 200 neon tetras, that aquarium no longer has enough beneficial bacteria to immediately convert all that waste into safe nitrates.

How can I increase my biological filter?

We naturally want to know how we can ensure enough biological filtration to manage toxic nitrogen compounds in our aquariums. One easy way is to of course add more aquarium plants, which will happily consume the ammonia and nitrates produced by your fish’s waste. 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.

As for growing beneficial bacteria, there is a common misconception that buying bigger or more filters will increase the amount of bacteria in your aquarium. Beneficial bacteria can grow on all surfaces in an aquarium. This includes glass walls, gravel, decorations, and even glass walls. Buying more filtration simply means you have greater capacity to hold more beneficial bacteria, but if you only have a few fish, your decor alone may have enough surface area to colonize the necessary beneficial bacteria.