Cycling Your Aquarium Without Fish: A Comprehensive Guide for Fishless Cycling

Aquarium cycling is an essential process for any new aquarium setup, ensuring a stable and healthy environment for your aquatic inhabitants. Fishless cycling is a popular method that eliminates the need for live fish during the cycling process, allowing beneficial bacteria to establish without harming any creatures. This comprehensive guide will explain the steps involved in cycling your aquarium without fish and how aquatic plants can play a vital role in the process.

What Is Aquarium Cycling?

Aquarium cycling refers to establishing beneficial bacterial colonies that convert harmful ammonia into less toxic compounds. This process is known as the nitrogen cycle and involves three key stages:

  1. Ammonia Production: Ammonia is produced by fish waste, decaying plant matter, and uneaten food. It is highly toxic to fish and other aquatic life.
  2. Nitrite Conversion: Bacteria known as Nitrosomonas convert ammonia into nitrites, which are less toxic but still harmful to fish.
  3. Nitrate Production: A second type of bacteria, Nitrobacter, converts nitrites into nitrates, which are relatively harmless in low concentrations.

Fishless cycling involves introducing ammonia into the aquarium without live fish to allow these bacterial colonies to grow and establish.

Steps for Fishless Cycling

Step 1: Prepare Your Aquarium

Before beginning the fishless cycling process, set up your aquarium with all the necessary equipment, including a filter, heater (if required), and lighting. Ensure the aquarium is clean and free of any contaminants. Fill the tank with dechlorinated water, as chlorine can kill beneficial bacteria.

Step 2: Introduce Ammonia

To cycle your aquarium without fish, you need to introduce a source of ammonia. This can be done using pure ammonia (without additives or fragrances) or fish food. If using pure ammonia, carefully add it to the aquarium until the ammonia concentration reaches 3-5 ppm (parts per million). If using fish food, add a small pinch daily until the ammonia levels rise.

Step 3: Monitor Ammonia and Nitrite Levels

Regularly test the water for ammonia and nitrite levels using aquarium test kits. Initially, the ammonia levels will be high, but as beneficial bacteria grow, they will convert ammonia to nitrites. Nitrite levels will then rise as ammonia levels decrease. This phase typically lasts 1-2 weeks.

Step 4: Introduce Aquatic Plants

Aquatic plants play a significant role in fishless cycling by absorbing some of the ammonia and nitrates, helping to stabilize the environment. Plants also provide additional surface area for beneficial bacteria to colonize. Consider adding fast-growing plants like Java Fern, Anubias, or Water Sprite, as they efficiently absorb nutrients and contribute to a balanced ecosystem.

Step 5: Wait for Nitrites to Convert to Nitrates

As beneficial bacteria continue to grow, nitrite levels will start to decrease, indicating that they are being converted to nitrates. This stage may take another 1-2 weeks. Continue to monitor the water parameters, and ensure that ammonia and nitrites are both at zero before proceeding to the next step.

Step 6: Conduct a Final Test and Perform a Water Change

Once ammonia and nitrites are undetectable, and nitrate levels have stabilized, conduct a final test to ensure the cycle is complete. If ammonia and nitrite levels remain at zero, perform a water change to reduce nitrate levels to 20 ppm or lower. This ensures a safe environment for your fish and aquatic plants.

Step 7: Introduce Fish Gradually

After completing the fishless cycle, you can introduce fish to your aquarium. Start with a few hardy species, allowing the biological filter to adjust to the increased bio-load. Gradually add more fish over several weeks to avoid overwhelming the established bacterial colonies.

Benefits of Fishless Cycling with Aquatic Plants

Fishless cycling offers several benefits compared to traditional fish-in cycling:

  • No Harm to Fish: By cycling without fish, you eliminate the risk of exposing fish to harmful ammonia and nitrites during the cycling process.
  • Faster Cycling: Fishless cycling allows you to add higher concentrations of ammonia, accelerating the establishment of beneficial bacterial colonies.
  • Aquatic Plants Help Stabilize the Cycle: Adding aquatic plants during fishless cycling provides additional benefits, such as absorbing excess ammonia and nitrates and providing extra surface area for beneficial bacteria to grow.


Cycling your aquarium without fish is a responsible and effective way to establish a healthy aquatic environment. By following the steps outlined in this guide, you can ensure a stable nitrogen cycle while leveraging the benefits of aquatic plants. Once the cycle is complete, you can introduce your fish to a safe and thriving aquarium. Remember to monitor water parameters regularly and maintain a healthy environment for your aquatic inhabitants.