Nitrogen Cycle in Aquariums – How to Cycle a Tank With Fish?

Are you just starting out as a fish parent? If so, you likely came to this page after learning about the nitrogen cycle in aquariums. You don’t need to panic, though the graphs and obscure scientific lingo may initially seem intimidating. I’ll walk you through all you need to know about the nitrogen cycle in aquariums.

This article will teach you just how to cycle your tank, enabling you to provide a happy and healthy habitat for your aquatic creatures.

What is the Nitrogen Cycle?

 The nitrogen cycle, simply put, is a chain of biological events that produce chemical reactions. Ammonia is created by the decomposition of food and fish waste. Ammonia is extremely harmful to fish and will eventually kill them in an aquarium. Ammonia, on the other hand, is “food” for nitrifying bacteria present in water.

By “eating” the hazardous ammonia, the nitrifying bacteria create nitrite. A different type of nitrifying bacteria “eats” the hazardous nitrite to create the less hazardous byproduct nitrate. The biological food chain balances out the damaging effects of ammonia and nitrite since nitrate unless it builds up in huge amounts, is generally safe for fish to consume.

Nitrogen Cycle

You must filter your aquarium water and change a portion of it on a regular basis in order to maintain nitrate levels that are safe for your aquatic life. Water’s chemical equilibrium must remain stable for fish and plants to live. This is maintained via the nitrogen cycle.

It is crucial to routinely test the water in your aquarium and make any necessary adjustments by performing a water change, adding or removing activated carbon, ammonia neutralizers, or water conditioners based on the results of your tests.

How to cycle your tank with Fish?

There are several ways to complete a fishless cycle. But since you’re probably a novice, I advise using this easy method.


You must set up a situation where ammonia can be created. What do you do if there are no fish in the tank?

Start by adding a few fish food flakes to your tank as a very easy method to do this. The same quantity should be added as if you were feeding fish. This can be done once every 12 hours. You just need to wait at this point. As the flakes decompose, ammonia will be released into your system.

A test kit is required, and you should check the ammonia levels in your tank every few days. Additionally, the amount should be at least 3ppm (parts per million). Add more flakes and let them decompose if your tank isn’t producing enough ammonia. Try to keep the ammonia levels at 3 ppm by testing every other day. The ammonia will be consumed by growing nitrosamines. When it falls below 3ppm, you should refill them by adding more flakes.

Testing for Nitrites

Once your ammonia-testing week is up, it’s time to test for nitrites. For this, you can utilize a test kit from a store.

Nitrite levels in your tank will let you know when the cycle has begun. Ammonia addition should proceed as previously.

When the nitrite levels start to decline after a few weeks of ammonia and nitrite testing, it’s time to move on to nitrate testing. This is a sign that the cycle is almost done when it occurs.

The cycle is finished when both the ammonia and nitrite levels have reached zero. To lower this figure, you’ll need to perform some water changes if your nitrate measurement is higher than 40.

Adding your Fish

It’s okay to start adding fish now that you can’t smell any ammonia or nitrite.

Once more, don’t just add a bunch of fish. This must be done gradually. Don’t introduce more than a few fish at a time, as was previously suggested. And before adding more, hold off for at least a week or two.

Adding your Fish

Before adding fish, think about using a siphon or hose to clean any substrate. There can be food inside that has started to rot. The ammonia won’t enter your tank’s water if it’s trapped; nevertheless, if it’s disturbed, it may swiftly release a dose of undesired ammonia.

How long does it Take?

It varies, but generally speaking, it can take a few weeks to months. By purchasing a vial of live nitrifying bacteria, borrowing some used filter media from a friend, or cultivating live plants, you can hasten this process (which also comes with beneficial bacteria on them).

Most people assume that when asked whether an aquarium has been cycled, the typical hobbyist will answer either categorically yes or categorically no. The solution itself is a little more difficult. What really needs to be asked is whether there are enough good bacteria in the tank to handle the trash the fish produce. For instance, the aquarium won’t have enough helpful bacteria to quickly convert all of that waste into innocuous nitrates if 200 neon tetras are suddenly added to a “cycled” aquarium with 3 neon tetras.

How do I increase Biological Filtration in my Fish Tank?

This begs the question of how to ensure that the aquarium has adequate biological filtration to handle harmful nitrogen molecules. Increasing the number of aquarium plants is an easy option since they will happily consume the ammonia and nitrates created by your fish waste. Remember that if you don’t have enough fish waste to feed your plants, they might starve to death, so supplement with a terrific all-purpose fertilizer like Easy Green.

Biological Filtration in my Fish Tank

It’s a common misconception that adding more or bigger filters would increase the number of beneficial bacteria in your aquarium. Every surface of your aquarium, including the gravel, glass walls, and decorations, may contain healthy microorganisms. If you merely have a few fish, however, your décor could be sufficient to support the necessary good microorganisms. Simply increasing the capacity of your tank to accommodate more beneficial bacteria is what additional filtration does.

The Bottom Line on Nitrogen Cycle in Aquariums

The most crucial thing you must do when using a fish-in cycle is to consistently monitor the parameters of your water quality. Since your fish must have no ammonia to be safe, you must keep ammonia levels as low as you can by doing frequent water changes until you have a sufficient population of nitrifying bacteria.

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