Nitrifying bacteria in aquariums: powering the nitrogen cycle as the key to a healthy tank

Whether you’re a beginner or a seasoned aquarist, you’ve likely heard about nitrifying bacteria. These tiny organisms are the unsung heroes of a thriving aquarium, keeping the water safe for your fish and plants. In this article, we’ll break down what nitrifying bacteria are, how they work, why they’re so important, and how to create the perfect environment for them in your tank. Let’s dive into the world of aquarium care and discover how to maintain a healthy ecosystem with these essential microbes!

What are nitrifiers and what do they have to do with ammonia? #

Nitrifying bacteria are microscopic organisms that live in your aquarium and play a vital role in keeping the water clean and safe. They’re a cornerstone of the nitrogen cycle, the natural process that ensures a balanced and healthy aquarium environment. These bacteria convert harmful compounds like ammonia and nitrites into less toxic nitrates, creating a safe home for your fish and preventing issues like algae blooms or poor water quality.

In aquariums, we commonly talk about two key types of nitrifying bacteria: Nitrosomonas and Nitrobacter.

• Nitrosomonas convert ammonia into nitrites, which are still toxic but less harmful than ammonia.
• Nitrobacter turn nitrites into nitrates, which are much safer for fish and can even serve as nutrients for aquatic plants.

Both types are critical for a properly functioning nitrogen cycle. Without them, ammonia from fish waste, decaying matter, or uneaten food would quickly build up and poison your tank.

Why nitrifying bacteria matter in your aquarium #

Think of your aquarium as a small, self-contained ecosystem. Everything from feeding your fish to the breakdown of organic matter affects water quality. Nitrifying bacteria act as natural cleaners, stabilizing the water and preventing cloudiness. Here’s why they’re so important:

• Protecting fish from toxins: Ammonia and nitrites are highly toxic to fish, causing stress, illness, or even death. Nitrifying bacteria neutralize these threats.
• Maintaining water parameters: By keeping nitrate levels in check, these bacteria make it easier to manage your tank’s water quality.
• Supporting plant growth: Nitrates, the end product of the nitrogen cycle, act as a nutrient for aquatic plants, promoting healthy growth.
• Reducing water changes: Efficient bacteria mean fewer harmful compounds, so you won’t need to change the water as often, saving you time and effort.

How does the nitrogen cycle work in an aquarium? #

Before we get into practical tips, let’s take a quick look at how the nitrogen cycle works. It’s a simple but crucial process driven by nitrifying bacteria. Here’s a step-by-step breakdown:

1. Ammonia production: Ammonia builds up from fish waste, uneaten food, decaying plants, or other organic matter. It’s highly toxic and needs to be neutralized quickly.
2. Ammonia to nitrites: Nitrosomonas bacteria oxidize ammonia into nitrites, which are less toxic but still harmful to fish.
3. Nitrites to nitrates: Nitrobacter bacteria convert nitrites into nitrates, which are safer in low amounts and can be used by aquatic plants as a nutrient.
4. Denitrification: In some tanks, especially those with advanced biological filters, denitrifying types of bacteria convert nitrates into nitrogen gas, which escapes the water. This requires low-oxygen conditions.
5. Nitrate removal: Nitrates accumulate over time and must be removed through regular water changes or absorbed by aquatic plants to prevent excessive buildup.

This cycle runs continuously as long as your tank has healthy nitrifying bacteria and the right conditions, like steady water flow and adequate oxygen. If you would like to learn more about the nitrogen cycle, we invite you to read this article.

How to introduce beneficial bacteria to your new tank (and avoid new tank syndrome) #

If you’re setting up a new aquarium, nitrifying bacteria won’t magically appear in large enough numbers on their own. They need time, the right environment, and sometimes a little help to thrive. Here are some effective ways to introduce them to your tank:

1. Use bacterial supplements
Commercial bacterial supplements contain live cultures of nitrifying bacteria, making them perfect for new aquarium owners. These products jumpstart the nitrogen cycle by colonizing your filter, substrate, and other surfaces. Always follow the manufacturer’s instructions regarding adding bacteria and choose high-quality products for the best results. In our assortment you can find products like: Bio S, Pro Bio S, -NP Pro, Hybrid Pro Salt and Life Bio Fil. In case of freshwater aquariums: AF Life Essence.

Check out also our video material about Life Bio Fil.

2. Transfer filter media
If you have access to a healthy, established aquarium, you can borrow some filter media (like a sponge or ceramic rings). These already contain active bacteria that will multiply and quickly adapt to your tank.

3. Cycle the tank naturally
This method requires patience but works well. Set up your aquarium and let it run without fish for 3–6 weeks. During this time, nitrifying bacteria will naturally develop. To speed things up, add a small amount of fish food to break down and produce ammonia.

4. Add aquatic plants
Plants not only absorb nitrates but also provide surfaces for bacterial growth. A tank with plenty of plants often has a more stable nitrogen cycle, keeping the water clear and balanced.

How to support nitrifying bacteria growth #

Nitrifying bacteria are sensitive to their environment, so you’ll need to create the right conditions for them to thrive. Here’s how:

• Proper filtration: Nitrifying bacteria often settle in biological filters, where they get steady water flow and oxygen. Choose a filter that supports water stability, and clean the media regularly – but never replace it all at once, as this could wipe out your bacterial colonies.
• Adequate oxygen: These bacteria need oxygen to perform nitrification. Ensure your water is well-aerated using a diffuser, air stone, or cascading filter (below 2-3 mg/L of dissolved oxygen nitrification won’t occur).
• Stable temperature: Most nitrifying bacteria thrive at 24–28°C (75–82°F). Too low or too high water temperature can slow their activity. If the topic of aquarium temperature is interesting to you check out this article.
• Avoid harsh chemicals: Some aquarium medications, chemicals, or sudden changes in water parameters (like pH levels) can harm bacteria. Always read product labels and dose carefully.
• Regular water changes: Weekly water changes (about 10% of the tank’s volume) help remove excess nitrates and maintain ideal conditions for bacteria. Check out our article on water changes to learn why it’s so important.

Common mistakes causing various aquarium problems #

New aquarium owners often make mistakes that can disrupt nitrifying bacteria and the nitrogen cycle. Here are a few to avoid:

• Adding fish too soon: A new tank needs time to cycle. Adding new fish right away can lead to ammonia and nitrite spikes, harming both fish and bacteria.
• Overfeeding: Excess food decomposes and produces too much ammonia, overwhelming your bacteria. Feed sparingly and remove uneaten food.
• Cleaning filters with tap water: Chlorine in tap water can kill nitrifying bacteria. Rinse filter media in tank water instead.
• Skipping water tests: Regularly test for ammonia, nitrites, nitrates, and pH to ensure the nitrogen cycle is working and catch issues early.

How to monitor nitrifying bacteria #

You can’t see nitrifying bacteria, but you can track their performance by testing your water. Aquarium test kits (drop or strip tests) measure ammonia, nitrites, nitrates, and pH. Here’s what the results mean:

• High ammonia levels: The nitrogen cycle hasn’t started, or the bacteria aren’t working properly. Check your filter, aeration, and avoid feeding fish for a few days.
• High nitrite levels: Nitrosomonas bacteria are active, but Nitrobacter bacteria haven’t caught up yet. Be patient as the cycle progresses.
• Nitrates present, no ammonia or nitrites: Congratulations! Your tank is fully cycled, and the nitrogen cycle is functioning perfectly.

How to support denitrification #

Beyond nitrifying bacteria, denitrification can further improve your tank by removing nitrates. This process happens in low-oxygen environments, like deep substrate layers or specialized filters, where denitrifying bacteria convert nitrates into nitrogen gas that escapes the water. To support denitrification:

• Use a thicker substrate layer to create low-oxygen zones for denitrifying bacteria.
• Invest in filter media designed for denitrification.
• Add more aquatic plants to absorb nitrates and enhance water stability.

Wrapping up #

Nitrifying bacteria are the invisible heroes of every aquarium, breaking down ammonia and nitrites into safer nitrates to keep your water clean and your fish healthy. Success comes down to patience, a reliable biological filter, steady water flow, adequate oxygen, and regular water changes. A new aquarium takes time to mature, but with the right care, your nitrifying bacteria will thrive, creating a balanced and vibrant ecosystem for your aquatic pets.