Cycling an Aquarium: The Essential Guide to a Thriving Underwater World

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Starting an aquarium is an exciting journey into the underwater realm, but before your fish can dive into their new home, there’s a crucial step every aquarist must undertake: cycling the aquarium. This process, also known as the nitrogen cycle, ensures a safe and stable environment for your aquatic pets. In this blog, we’ll guide you step-by-step through the art of cycling, ensuring your fishy friends thrive and flourish.

Understanding the Nitrogen Cycle

At the heart of a thriving aquarium lies a balanced ecosystem, and the nitrogen cycle plays a pivotal role in achieving this balance. Here’s a simplified breakdown:

  1. Ammonia Production: Fish waste, uneaten food, and decaying organic matter produce ammonia (NH3) – a toxic compound for most aquatic life.
  2. Conversion to Nitrite: Beneficial bacteria called Nitrosomonas break down ammonia into nitrite (NO2), which is also toxic but a step closer to a safer environment.
  3. Conversion to Nitrate: Another set of beneficial bacteria, Nitrobacter, further convert nitrite into nitrate (NO3). While nitrate is less harmful than its predecessors, it still needs to be kept in check through regular water changes.

How to Cycle Your Aquarium

1. Setting Up: Begin by setting up your aquarium with all equipment (filters, heaters, etc.) and add water. It’s a good idea to use a water conditioner to neutralise chlorine or chloramine, which can hinder the growth of beneficial bacteria.

2. Kick-starting the Cycle: There are several methods to introduce ammonia into the tank:

  • Fishless Cycling: Add a source of ammonia, such as pure liquid ammonia or raw shrimp. This method avoids subjecting live fish to harmful conditions.
  • Using Fish: Some aquarists use hardy fish species to produce ammonia naturally through their waste. However, this method is debated due to the stress it places on the fish.
  • Bottled Bacteria: Available in pet stores, these can speed up the process by introducing beneficial bacteria directly.

3. Monitoring: Regularly test the water using an aquarium test kit. Track the levels of ammonia, nitrite, and nitrate. The cycle is complete when ammonia and nitrite levels drop to zero, and you see a spike in nitrates.

4. Water Changes: Once you detect nitrates and the levels of ammonia and nitrite are zero, perform a large water change (50-70%) to reduce nitrate concentration.

5. Introducing Your Fish: Slowly introduce your fish to the cycled tank. Remember to acclimatise them properly to avoid shock.

Tips for a Successful Cycle

  • Stay Patient: The cycling process can take anywhere from 2-8 weeks. Patience is key!
  • Avoid Overcrowding: Once cycled, introduce fish gradually. Adding too many fish at once can cause an ammonia spike.
  • Maintain Your Cycle: Regular water changes, filter maintenance, and avoiding overfeeding will help maintain a stable nitrogen cycle.


Cycling your aquarium might seem daunting at first, but with patience and understanding, it’s a task that can be both educational and rewarding. It lays the foundation for a healthy and harmonious aquatic environment, ensuring your fish live long, happy lives. As you embark on this aquatic journey, remember: the beauty of a thriving aquarium is well worth the wait!

Whether you’re a beginner in Australia or an experienced aquarist anywhere in the world, understanding the nitrogen cycle is crucial. Dive deep into the world of fish-keeping with a strong start, and watch your underwater haven flourish!

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