The Nitrification Cycle in Aquaponics: How to Cycle Your System Safely
Before your plants can thrive and your fish can stay healthy, your aquaponics system needs one invisible hero working behind the scenes: the nitrification cycle.
Understanding the Nitrification Cycle
Every aquaponics system relies on one invisible process: the nitrification cycle.
It’s what transforms fish waste into plant food and keeps your water clean and balanced.
This cycle is what makes aquaponics so sustainable—it’s nature’s own recycling system, recreated in a man-made design.
By learning how it works, you can avoid common beginner mistakes, protect your fish, and create a thriving mini-ecosystem.
Find out more about understanding the nitrification cycle in aquaponics.
What Is the Nitrification Cycle?
The nitrification cycle is the biological process where beneficial bacteria convert toxic fish waste into safe, plant-available nutrients. It’s the natural foundation of every aquaponics system—and it’s exactly what happens in rivers, lakes, and wetlands all over the world.
In your system, there are two main types of bacteria at work:
1. Nitrosomonas – These bacteria convert ammonia (NH₃), which comes from fish waste and uneaten food, into nitrite (NO₂⁻).
This is the first step of the cycle, but nitrite is still harmful to fish.
2. Nitrobacter (and closely related Nitrospira) – These bacteria then convert nitrite (NO₂⁻) into nitrate (NO₃⁻).
Nitrate is much less toxic and becomes a valuable nutrient for plant growth.
Together, these bacteria form the biological engine that keeps your aquaponics system clean and self-sustaining.
In the wild, these bacteria naturally live in soil, riverbeds, and pond surfaces. In aquaponics, we’re simply replicating nature in a man-made design—encouraging these same species to colonise the surfaces of our grow media, pipework, and filters.
Tip: If your system is indoors, this process can take longer because your home is a closed environment. There’s less natural bacteria floating in the air to “seed” your system, so you may need to add a bacterial starter to help things along.
When this cycle is fully established, you have a balanced system where fish, plants, and bacteria all support one another.
Watch this video on What Is the Nitrification Cycle in Aquaponics (and How It Works With Examples)
Cycling Your System (Starting the Bacteria)
Cycling means building up the bacterial colonies that handle waste conversion.
It’s the very first step in any new aquaponics setup—and one that’s often rushed or skipped.
There are two main ways to cycle your system:
1. Fishless Cycling (Recommended)
This method allows you to safely grow your bacteria before adding fish.
It’s more humane, easier to control, and gives you a head start.
How to do it:
Add an ammonia source – This can be pure household ammonia (without additives), fish food, or a bacterial starter product.
Monitor your readings daily using test kits for ammonia, nitrite, and nitrate.
At first, you’ll see ammonia rise, then nitrite appear, and finally nitrate.
The process usually takes 3–6 weeks, depending on the temperature.
(Warmer water around 24–28°C / 75–82°F speeds things up.)When ammonia and nitrite consistently read 0 ppm, and nitrate is present, your system is fully cycled.
2. Cycling With Fish (If You Already Have Them)
If you already added fish before the bacteria developed, don’t panic—just support the cycle carefully.
What to do:
Add beneficial bacteria immediately (available at aquarium or aquaponics suppliers).
Test your water daily for ammonia and nitrite.
If levels rise, do partial water changes (20–30%) using dechlorinated water.
Feed lightly until the cycle stabilises. Overfeeding increases ammonia faster than bacteria can process it.
This method takes more patience but can still succeed with careful monitoring.
Why Dechlorination Is Essential
If you’re using tap water, always remove chlorine or chloramine before filling your system.
These chemicals are designed to kill bacteria, which means they’ll destroy the very bacteria you’re trying to grow.
Ways to remove chlorine:
Let water sit for 24–48 hours before use with an airstone in the water (sunlight helps).
Use a dechlorinator that’s safe for fish and aquaponics.
If your council water contains chloramine, you’ll need a conditioner specifically designed to break it down.
Skipping this step is one of the most common reasons cycling fails.
Watch this video on How to Cycle Your Aquaponics System Step-by-Step
Tips for a Smooth Cycling Process
Test Daily During the Cycle
Record your ammonia, nitrite, nitrate, and pH readings. You’ll literally see the cycle unfold in front of you.
Add Air and Warmth
Beneficial bacteria need oxygen and steady warmth to thrive. Keep your water well-aerated and around 24–28°C (75–82°F) if possible.
Be Patient
Try not to rush this stage. Giving your bacteria time to establish properly can save you a lot of stress later. If you add plants too soon, they can use the fertiliser and affect your readings. I like to wait until I am getting small readings of nitrate before I add plants. That way, I know that both bacteria are present and growing a bigger colony.
Feed Sparingly
Too much food = too much waste = dangerous ammonia spikes.
Don’t Clean Everything
Once your system is running, never wash your bio-filter or grow media with tap water.
Always rinse gently in tank water to protect your beneficial bacteria.
Want a Simpler Way to Start Your Aquaponics Journey?
Getting your aquaponics system started can feel a little overwhelming at first, especially when you’re learning about water quality, bacteria, fish, plants, and cycling all at once.
That’s why the free Urban Aquaponics eBook is a helpful next step. It walks you through the basics, helps you understand whether aquaponics is right for you, and gives you simple information to start your journey with more confidence.
Get inspired to start your journey today.
Get your free copy HERE
Recognising When Cycling Is Complete
Your system is cycled when:
Ammonia: 0 ppm
Nitrite: 0 ppm
Nitrate: rising and detectable (20–80 ppm)
pH: stable between 6.8–7.2
At this point, your bacteria are established, your water is balanced, and you’re ready to slowly increase your fish and plant numbers.
Common Aquaponics Cycling Problems and How to Fix Them
A Balanced Ecosystem
Cycling is all about replicating nature.
In the wild, streams and ponds already contain bacteria that manage waste, but in aquaponics, you’re recreating that balance in a man-made design.
When you take time to establish this natural foundation, everything that follows—healthy fish, strong plants, clear water—flows easily.
Learn More About Aquaponics
Check out the COURSES page to learn how you can get started with aquaponics now. Click HERE.
Want to get your Eyes and Hands on the FREE Online Aquaponics Essentials Course?
This is a great free resource to really understand how aquaponics is a sustainable ecosystem that will grow your organic food is a productive way.
You learn how all the 'parts' make up the 'whole', and helps to give you the foundations of understanding aquaponics.
Sign up HERE
Check out my YouTube Channel 'Candy The Aquaponics Lady'
Aquaponics is an ecosystem, and with anything it takes time to learn how it works. So, sit back and binge watch my 'how to' playlist and the 'Water Quality Made Simple' Playlist, and learn the next steps in your aquaponics system as you create the ecosystem.
Here are the next 2 videos I recommend you watching to create your ecosystem ~ before you add any fish
How Aquaponics Works as an Ecosystem
Why aquaponics is the best form of gardening for you
Learn More About Aquaponics
Check out the COURSES page to learn how you can get started with aquaponics now. Click HERE.
Want to get your Eyes and Hands on the FREE Online Aquaponics Essentials Course?
This is a great free resource to really understand how aquaponics is a sustainable ecosystem that will grow your organic food is a productive way.
You learn how all the 'parts' make up the 'whole', and helps to give you the foundations of understanding aquaponics.
Sign up HERE
Want to help out (donate some fish food) and Feed my Fish?? (They don't drink coffee)
Candy Alexander is a dedicated aquaponics enthusiast with a wealth of formal training in aquaculture. Over the past 15 years, Candy has been deeply immersed in both commercial and backyard aquaponics, honing her skills and expertise in this sustainable farming method.
Candy's passion lies in making aquaponics accessible to everyone. With a mission to simplify aquaponics, she believes that anyone can embark on this sustainable journey.
She encourages those new to aquaponics to "kick the tires" without a significant financial investment. Her guidance focuses on helping people start their aquaponics journey with small-scale systems, ensuring a low barrier to entry for newcomers.
Candy shares practical tips, step-by-step guides, and personal stories to inspire and guide readers on their aquaponics adventure. Whether you're a seasoned farmer or a curious beginner, Candy Alexander is your go-to source for simplifying aquaponics and fostering a sustainable gardening experience.
