How to Cycle a Fish Tank

Looking to ensure the success of your planted aquarium? The initial stages of tank setup play a vital role. Understanding the underlying science that supports the well-being of your aquatic plants and their animal companions can be highly beneficial.

Among the crucial steps in tank setup, cycling is paramount. Familiarizing yourself with the nitrogen cycle is essential for maintaining a harmonious and thriving aquarium environment for fish, shrimp, and plants. This natural process involves the conversion of harmful ammonia, generated by waste and decaying matter, into less toxic compounds like nitrite and nitrate. 

This article will go over:

  1. The nitrogen cycle 
  2. The importance of a cycled tank
  3. The best way to cycle your tank

What is the nitrogen cycle? 

Let's delve deeper into the nitrogen cycle to develop a comprehensive understanding of how nitrogen influences your aquarium. Many of you may recall learning about nitrogen during your school days. Nitrogen is a chemical element that constitutes approximately 78% of the Earth's atmosphere. It plays a vital role in various physiological processes in living organisms. However, excessive concentrations of nitrogen in the form of ammonia, nitrite, and nitrate can be toxic to aquatic life, with ammonia being the most toxic, followed by nitrite, and nitrate being the least toxic.

Nitrogen is a byproduct of protein degradation. In the context of your aquarium, this refers to the breakdown of fish waste, uneaten food, decaying plants, and other organic matter accumulating in your tank. This decomposition process results in the release of ammonia, which then undergoes conversion to nitrite and ultimately nitrate.

It is crucial to maintain a balanced nitrogen cycle in your tank to prevent harm to your aquatic inhabitants. Elevated levels of ammonia above 0.0 ppm can pose a significant threat to the well-being of your tank's occupants.

 nitrogen cycle for fish tank
The Nitrogen Cycle

Why is a cycled tank important?

In a natural environment with a large body of water, ammonia is typically diluted quickly and does not pose any harm to living organisms. However, in your aquarium, ammonia, the most toxic form of nitrogen, can accumulate easily and create an unhealthy living environment for both your plants and animals.

This is why 'cycling your tank' is crucial for maintaining a healthy aquarium. A cycled tank indicates that an active and balanced nitrogen cycle is taking place. It means that beneficial bacteria, which facilitate the nitrification process, have established and colonized in your tank. In an established or cycled aquarium, the beneficial bacteria residing mainly in the filter media swiftly convert ammonia (more toxic) to nitrite (toxic). Nitrite, although less toxic than ammonia, can still be harmful in high concentrations. The nitrite in the tank is then further converted to nitrate (less toxic) by the beneficial bacteria within the filter media. You can learn more about different types of filters and the importance of filtration in our related article.

While nitrate is the least harmful form of nitrogen and can be tolerated in higher amounts, it still needs to be removed through regular water changes. Performing frequent water changes is the best way to reduce nitrogen buildup in your tank, so make sure to stay consistent with your water change routine. (You can find detailed information on how to perform water changes correctly in our guide.)

Furthermore, aquatic plants play a crucial role in absorbing and utilizing nitrate for growth. By incorporating an abundance of aquatic plants in your tank, you can help lower nitrate levels. Having an ample amount of plants not only enhances the aesthetic appeal of your aquarium but also contributes to creating a natural ecosystem, aiding in maintaining the chemical balance within your tank.

What’s the best way to cycle my tank?

Now that you have a thorough understanding of the significance of the nitrogen cycle, let's discuss how to establish a balanced cycle in your aquarium, commonly referred to as "cycling your tank."

  • Keep in mind that maintaining an ammonia level above 0.0 ppm can be harmful to the inhabitants of your tank. To ensure that your tank is fully cycled, it is essential to utilize a freshwater test kit to monitor the water parameters. A properly cycled tank should exhibit the following parameters:
ammonia levels cycled tank

Fishless Cycles (recommended)

To initiate the nitrogen cycle in your new tank, there are several recommended methods, particularly the 'fishless cycles.' These methods involve growing beneficial bacteria in your tank's filter before introducing any fish or other animals, prioritizing the well-being of your aquatic companions.

Here are the top three ways to cycle your aquarium:

1. Allow your tank to run without any livestock (plants, fish, shrimp, etc.) after setting it up with substrate and hardscape until it becomes established.

  • During this period, occasional "ghost feedings" are performed to generate ammonia from uneaten food, promoting the colonization of beneficial bacteria. These bacteria naturally enter the tank from the surrounding environment, such as the air, hardscape, and substrate.
  • This method is the slowest and may take approximately 1-2 months.

For a more efficient cycling process, direct addition of bacteria can be implemented using the following methods:

2. Incorporate liquid nitrifying bacteria into the tank regularly.

  • Following the proper dosing instructions provided by the product, this approach accelerates the formation of the nitrogen cycle.

3. Introduce filter media from an established tank to your new tank's filter.

  • By doing so, you encourage the rapid colonization of beneficial bacteria and ensure proper cycling. However, it is essential to use filter media from a trusted source to prevent unwanted pests and pathogens from entering your new tank.
  • Running the new filter alongside an already established filter (side-by-side) can also expedite the colonization of the new filter.
  • Note: Take care not to let the filter media dry out during the transfer process. Transfer it quickly from the established tank to the new tank to prevent the beneficial bacteria from dying due to drying out. Methods 2 and 3 significantly reduce the cycling time to approximately 1-3 weeks

Fish-In Cycle (not recommended)

The final method to cycle a tank is known as the "fish-in cycle," but it is not recommended.

This approach involves adding a few hardy fish to the tank, which leads to the production of ammonia for the nitrifying bacteria. However, during the initial stages, there may not be enough bacteria colonies to efficiently convert all the ammonia to nitrate. High concentrations of ammonia can be harmful to the fish and plants in the tank, making the fish-in cycle unfavorable and should be avoided.

Cycling your aquarium is essential to prevent harm to your tank's inhabitants. Once your tank has been properly cycled, beneficial bacteria will thrive in your filter media, ensuring the continuous nitrification cycle.

It is crucial to establish and maintain a healthy population of beneficial bacteria in your tank. Regular testing of your tank water and consistent water changes are necessary to maintain a balanced and thriving cycled tank and its inhabitants. Remember, patience is key, so plan accordingly. 

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