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After you set up your aquarium and add water, the next most crucial step is to make sure you cycle your aquarium.

A lot of people feel intimidated by this process. Still, it’s not that difficult, and the infographic below does a great job visually simplifying the nitrogen cycle and breaking it down into five super-simple steps.

It’s crucial to make sure you get beneficial bacteria growing which is needed to provide biological filtration and keep your ammonia and nitrite levels near zero and your nitrate levels below 40ppm

Products To Help Start Nitrogen Cycle & Bacteria Growth

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3 Stages Of The Fish Tank Nitrogen Cycle

To put it simply, the nitrogen cycle is just a series of steps where bacteria convert harmful waste into something less toxic.

Before we go any further, it’s essential to discuss the three stages of the nitrogen cycle.

Stage 1: Ammonia Levels

In stage one, you are looking to create ammonia in your aquarium. This happens when your fish poops! The fish waste starts to produce ammonia. And lucky for you, ammonia is “food” for nitrifying Bacteria called Nitrosomonas, which then consume ammonia and convert it into Nitrites.

Stage 2: Nitrites

Once the ammonia has been converted into Nitrites, another beneficial bacteria called Nitrobacter steps in to consume the nitrites and turn it into less harmful Nitrates.

Stage 3: Nitrates

Lastly, once the beneficial bacteria convert the nitrites, you are left with the least harmful Nitrates. Nitrates are the final by-product of the nitrogen compounds and the last step of the cycle.

Overview Of The Nitrogen Cycle


Photo Credit: My Pet Warehouse

Here are the key takeaways from the infographic;

Step 1) Set Up Your Aquarium

In this step set up your aquarium as you typically would by adding your gravel, set up your equipment, add your decor, and fill your tank with water.

For a more detailed guide, check out our Ultimate Step by Step Guide Freshwater aquarium setup.

Step 2) Starting The Cycle

This can be done in one of two ways Fishless and Fish-In

While I’m not going to get into the debate of which option if more humane for the fish, I’ll leave that up to you to decide. I’m simply going to go over both options you have, and I’ll be honest with you.

I’ve done both the Fishless and Fish-In Cycle, and each has its pros and cons, which we’ll discuss next.

How To Do A Fishless Cycle:

There are a few ways to start a fishless cycle, the most common of which is done by adding ammonia or food to your tank. We’ll go over each one below;

Adding Ammonia & Food

This requires you to add a source of ammonia to the tank before any fish are in the aquarium. To do this, you can add some fish food or an ammonia additive, then wait for the cycle to start.

As the food break downs (Slowly), it will create ammonia, which is the first stage of the cycle, as mentioned above.

I don’t like this method, it takes a long time, and to be honest, I’ve never had any success and eventually end up using one of the other techniques below.

Cycle Your Tank With Plants

I like this method, mainly because I like planted tanks, but I usually combine it with one of the Fish-In cycle options below, but you can have success using this as a Fishless cycle option if that’s what you want.

Here’s what to do;

As you set up your new aquarium, plant a bunch of live Aquarium Plants. Then spend the next few weeks growing healthy plants. If you’ve never grown, live plants use this time to learn about lighting, substrates, Co2, and fertilizers.

Eventually, the plants will start to grow and use up any nitrogen compounds in your aquarium.

When you notice new growth, Its a pretty good signal that the cycle has finished.

To make sure, just test your water parameters, and if your ammonia and nitrites are at 0 ppm and you have some level of nitrates, your good to start adding some new fish slowly to your beautiful planted aquarium.

How To Cycle Your Tank With Fish

The second way to start the nitrogen cycle is to add some hardy fish, shrimp, or snails, but this can be harmful to the fish, and if not done correctly, you can lose a fish or two.

Here are two options I like to use:

1. Cycle With Old Filter Media

This is one of my favorite ways to jump-start the nitrogen cycle because it’s the fastest and safest way, in my opinion.

To do this, all you need is some old filter media from another aquarium. I’ve even used water from a water change on an established tank to fill the portion of the new tank.

Here’s what to do:

Just remove some biological media, or even the mechanical media, like a sponge from an established tank and place it into the filter on your newly set up aquarium.

That’s it; you’re done! Easy Right!

I also like to take the dirty sponge or filter floss and just place it into the new tank water and give it a few squeezes, which will send all the beneficial bacteria out into the water column to colonize everywhere in the new tank.

After I’ve used the old filter media, I still will wait for about 24hrs before adding any fish to the tank. But this beats waiting weeks, in my opinion.

Just be sure to add new fish slowly overtime adding no more than 2-3 fish at a time, so you don’t overload your tank.

2. Adding Live Nitrifying Bacteria

Adding live bacteria to your tank can be done in the way I described above by using old media from an established tank. But it can also be done another way.

Here’s what you do:

My Favorite Filter
AquaClear HOB Filter

The AquaClear HOB filter has been around FOREVER and is typically the first filter recommended for most beginners. That said, it's a great reliable filter for experienced fish keepers and Aquascapers. It comes with prepackaged filter media but also has the ability to customize to your needs. Don't worry about water flow as the gentle waterfall design creates oxygenation without a strong current perfect for small tanks and Bettas.

You’ll need to buy a live nitrifying bacteria product like Seachem Stability or Fritz Zyme.

I’ve used both and had success with both, so feel free to use your preferred product. In this case, just follow the instructions for each product before adding fish.

I believe both products advise that you can add fish after 24-48 hours, which is fine, just make sure you monitor your water parameters every other day to ensure the water quality is safe for your fish.

Step 3) Test The Water For Ammonia And Nitrites

Whichever way you choose to cycle your aquarium, you’ll need to watch for a few things.

You’ll need to check the water and monitor the ammonia levels and nitrites every few days and make sure to look for the spikes followed by the fall.

  • Ammonia will spike, then fall to 0 ppm
  • Nitrites will spike, then drop to 0 ppm
  • Nitrates will start to rise

Step 4) Wait Until Nitrates Rise 

As the Ammonia and Nitrites spike and then fall, you’ll notice the Nitrates begin to increase. The Nitrates will continue to grow until you complete a water change.

You’ll know the Nitrogen Cycle has completed when the ammonia and nitrite levels fall to zero, and you have some level of Nitrates.

It’s essential to do partial water changes to keep the Nitrates lower than 40ppm. Levels higher than this can start to harm the fish.

It can sometimes take up to three months before a new aquarium has cycled fully and converted the waste into Nitrates.

Step 5) Complete Partial Water Changes & Aquarium Maintenance

Depending on your stocking levels and if you have live plants, weekly water changes might be needed to remove excess nitrates.

To learn more about regular aquarium maintenance and water changes, check out: Aquarium Water Changes The Easy Way to learn more about doing a water change.

Common Questions About The Nitrogen Cycle

Below are some commonly asked questions about the Nitrogen Cycle, Beneficial Bacteria, Ammonia, and Tank Water.

How Long Does The Nitrogen Cycle Take In A Fish Tank?

It can take from 6 weeks up to 3 months to cycle your fish tank depending on many factors. But the real answer is that it will finish once the beneficial bacterial has established enough biological filtration needed specifically for your aquarium.

You just need to be patient and test your aquarium water every other day looking for the spike/fall of ammonia and nitrite, then finally the rise of your nitrates.

Is Nitrogen Harmful To Fish?

In nature, high levels of nitrogen compounds are pretty rare because of the established ecosystem that has evolved over thousands of years.

However, in your aquarium, it more likely you’ll find some level of nitrogen compounds due to many factors such as; fish waste, overfeeding, rotting organics. Over time these toxins will build up and eventually kill your fish.

This is where the Nitrogen Cycle comes to the rescue by establishing and allowing for your beneficial bacteria to grow and maintain suitable biological filtration.

Eventually, you’ll need to help keep these toxins at a manageable level with water changes to keep the water safe for your fish.

How Do I Know When My Tank Has Cycled?

You’ll know the nitrogen cycle has completed when the ammonia and nitrite levels fall to zero, and you have some level of Nitrates.

It’s essential to do regular water changes to keep the Nitrates lower than 40ppm as levels higher than this can start to harm the fish.

How Do I Increase My Biological Filtration?

You might be thinking to increase your biological filtration; you need to use a bigger filter or add more media.

This is partly true:

Of course, a bigger filter and more media will increase how much bacteria will colonize, but the beneficial bacteria in your aquarium will grow on everything in your aquarium. This includes the glass, substrate, decor, and of course, your filter media.

In most cases, if you’re not overstocking your tank, a properly sized filter, along with the natural colonization of everything in your tank, will be more than enough biological filtration for your tank.

Another thing you can do to help is by planting lots of aquarium plants.

Plants, as you know, will gladly use up excess ammonia and nitrates as food to help them grow, which ultimately can help reduce the toxins in your tank and extend the time between water changes.

Lastly, I believe most biological filtration is occurring in your gravel/substrate, and therefore if you have only a few fish with lots of plants, you might not even need a filter; think about that before you set up your next tank.

Fish Tank Nitrogen Cycle Simple Fundamentals (Tips To Add Fish Fast)