How to Cycle a Fish Tank? Step by Step

Most novice aquarists assume fishkeeping is all about assembling a tank, adding water, and dumping fish.

Whoa there, that’s not the way at all!

Before you begin your fishkeeping journey, your first responsibility will be to cycle your new fish tank. In other words, your tank needs to undergo the nitrogen cycle.

This essential step helps in creating a healthy environment for your aquatic buddies.

Now, you might say it sounds tedious and confusing. Of course, you also need to be extremely careful throughout the entire process.

No, don’t worry, it isn’t as complicated as it sounds. So, let’s learn everything about it here…

What is cycling a fish tank (aquarium cycling)?

In new tanks, aquarium cycling helps create a chemically and biologically safe environment for your fish and other tank inhabitants.

In this process, nitrifying bacteria are introduced into the tank, which helps in nitrogen cycle regulation. The said bacteria check the ammonia buildup and its effects due to fish waste decomposition.

The process converts ammonia into nitrite and, finally, nitrate.

What is the Importance of Aquarium cycling?

Beneficial nitrifying bacteria must be established in fish tanks before introducing fish. This way, they can deal with ammonia spikes and quickly convert them to less harmful nitrates.

Biofilters won’t be able to deal with the ammonia spike if fish are introduced too quickly or too many fish are introduced immediately after cycling.

In this case, there’s a toxin buildup, which results in New Tank Syndrome. Your fish may get hurt from it, especially if it’s not the hardy type.

What is Fishless Cycling Method?

You can cycle your tank in different ways. But the best option for beginners is without fish, aka fishless cycling. There’s also another cycling option – with fish or fish-in. We’ll explain more about it later on.

The fishless cycle is the most humane, popular, and safest way for your aquatic buddies. Here’s how you can do it:

Step 1: Set up your tank

Before you begin the process, assemble the tank with substrate and decor. Don’t add plants or fish. Check whether the following components are functional and keep them running:

  • Pumps
  • Bubblers
  • Heaters
  • Filters

This lets nitrifying bacteria accumulate on the tank surfaces, substrate, and filters. They reproduce and establish the nitrogen cycle.

Maintain a temperature range between 77-86 °F (25-30 °C). If you’re using tap water, treat it with a dechlorinator, as chlorine and chloramine kill the nitrifying bacteria. Get your hands on the necessary test kits to check ammonia, nitrite, and nitrate levels.

Step 2: Keep an eye on the pH

The ideal pH level for an efficient nitrogen cycle is 7-7.8. Test it regularly using pH test strips or all-in-one kits.

A pH less than 7 (acidic) undesirably raises ammonia levels.

On the other hand, a pH above 9 (alkaline) converts ammonium to ammonia and affects the tank environment. Both situations are detrimental to the nitrogen cycle.

Step 3: Introduce ammonia producers

A source of ammonia is necessary to begin the nitrogen cycle. For that, add the amount of fish food you’d require to feed all of your fish. This food will decay and release ammonia, which will begin the cycle.

Step 4: Track and maintain ammonia levels

After the food starts decaying, test the tank’s ammonia levels. The ideal range is 3-5 ppm.

Any less than 3 ppm won’t produce enough ammonia. You should add more fish food in that case.

If the ammonia level is higher than 5 ppm, perform a 10-20% water change with treated water to balance the levels.

Check the levels daily for a week and fine-tune things to keep them within the range.

Step 5: Test for nitrite levels

After maintaining a steady ammonia level for a week, the nitrite levels will slowly start rising. If it’s still undetectable, continue with the previous step for a few more days.

When the nitrite levels appear, they’ll spike pretty fast as there’s no regulator.

Meanwhile, continue to maintain the ammonia levels. The nitrites are formed from ammonia. If the ammonia level drops completely, you’ll need to begin from scratch.

Consistently add fish food so that there’s a steady amount of ammonia. Wait until there’s a drop in nitrite after it rises. You can then move on to the next step.

Step 6: Begin testing for nitrates

Once the nitrites drop after the sharp spike, check for nitrate levels. If it’s a detectable amount, it shows beneficial nitrifying bacteria have appeared. This declares the close to the end of the cycle.

Now, you must start adding half the amount of fish food you usually add – but only once every 2-3 days.

Keep testing ammonia, nitrite, and nitrate levels. The entire cycle ends once the tank shows zero ammonia and nitrite levels and a steady nitrate level.

Step 7: Slowly introduce your fish

The entire cycling process takes 6-8 weeks. Once you notice signs of the cycling coming to an end, slowly add 1-2 fish to your tank. This will avoid overwhelming the environment.

Once a week passes, and after that, test for ammonia levels. If it’s zero, you may add more fish slowly.

For a few days after that, steadily monitor and regulate all chemical levels to create a safe environment for your fish.

Is it possible to speed up the fishless cycling process?

Yes, if you’re impatient, you can also speed up the fishless cycling process with a few tips. However, beware that this comes with its own set of rules. So, it’s always advised to take the above-mentioned long route instead.

But if you’re careful enough, here are some ways to accelerate things:

1. Take the help of another established tank

There are a few options in this one, as follows.

Option A: Borrow the filter media from the established tank

Use the filter media from a previously established tank to introduce nitrifying bacteria to the new tank. Ensure you use the filter media of a tank of similar size and similar or more amount of fish.

This reduces the time taken to encourage bacterial growth naturally. Thus, it speeds things up.

Option B: Introduce some gravel from the established tank

You can also use a few scoops of gravel from the established tank and add them to the new tank. The bacteria sitting on the gravel will eventually multiply.

Option C: Get some live plants from the established tank

Take living plants from the established tank and plant them in the new one. Hygrophila and Vallisneria are preferred, but you can also try floating plants.

The plants can both carry beneficial bacteria from the original tank and absorb ammonia for their own protein synthesis.

Option D: Install another filter in the established tank

Alternatively, you can install the filter to be used in the new tank in the established one. Let the new filter run along with the existing filter(s) for 4-6 weeks.

Add some fish food for ammonia production in the new tank to work with. You can then introduce that newly-matured filter to the new tank.

Note: Test the established tank for parasites (like velvet and ich) and pests (like harmful algae and snails). Proceed with the above steps only if the established tank is free from pests and parasites.

2. Invest in OTC bacterial products

You can also buy bacteria in fish stores that have a few strains of beneficial nitrifying bacteria. These products jump-start the process.

Note: Some debate that these bacteria bottles might not contain all types of bacteria necessary for the proper cycling of your fish. Furthermore, it may still not accelerate the process magically.

3. Use ammonia directly

Rather than adding fish food to release ammonia, set up your tank and add 5 drops of pure ammonia for every 10 gallons regularly. Once the nitrite levels become detectable, add 2-3 drops of ammonia regularly. Once nitrite levels become zero, your tank is cycled.

This process takes only a week to complete.


  • Ensure the tank is well-oxygenated for the nitrifying bacteria to thrive.
  • Use perfume and additive-free ammonia
  • Don’t treat water with conditioners, as that removes ammonia.

What are the Other Processes of Cycling a Fish Tank?

There are two other fish-tank cycling processes. But they are not favored for various reasons. C’mon, let’s get an idea for each here…

1. Fish-in Cycling Process

In fish-in cycling, you add only 1-2 extremely robust fish in an uncycled tank. The process induces an ammonia spike for the beneficial bacteria to thrive on using fish waste.

It includes lots of routine water changes along with tracking the levels of ammonia, nitrate, and nitrite.

Why is fish-in cycling not popular?

It is highly discouraged in the hobby, used only when there’s an emergency, and can be conducted by experts alone. Some reasons to avoid the fish-in cycling process are:

  • This takes much longer than any other method.
  • Beginners are prone to mistakes of overfeeding and overstocking. This spikes the ammonia levels uncontrollably. It puts excessive stress on the fish, which may even lead to the loss of fish.
  • By the end of the cycle, the water isn’t crystal clear, unlike the fishless process. It affects the aesthetics of the tank and even the health of your fish.
  • The process doesn’t produce much beneficial bacteria compared to the fishless cycle. Thus, you can’t add a lot of fish for months.

2. Cycling with Plants Process

In this, a tank is set up just like in the fishless cycle. Hardy plants are added to it after disinfecting them to prevent parasite and pest introduction in the tank.

With proper lighting, fertilizers, and water change routines, you have to wait for growth in plants and algae. This declares the end of cycling.

Why is cycling with plants not popular?

Some people say plants are better for consuming nitrogen waste than nitrifying bacteria. They also find it more humane than the fish-in cycle.

However, this is the least predictable process. Mistakes may lead to plant death or uncontrolled algae growth. This shows the cycle failed, and you’ll have to start from scratch.

A word from FishInAquarium

As a beginner, your best bet is fishless cycling, even if it takes time. Remember, the fishkeeping journey needs a lot of care and concentration. So, you will be able to create a stable, safe, and sustainable ambiance for your aquatic friends only with patience.

With that said, if you liked our guide, make sure to share it with other novice enthusiasts. Learn to cycle your tank together and share your successes and challenges. Motivate each other to build the aquarium of your dreams!

And if you face any trouble, drop us an email, and we’ll connect with you soon!

Minnie B Miller - Professional aquarist and owner of FishInAquarium

About Minnie B Miller

Minnie B. Miller, a professional aquarist and owner of FishInAquarium, has over 8 years of expertise in fish breeding and care, gained through her roles at AquaticTX and Sea Lion Landing. Having honed her skills with various aquatic species, she is dedicated to empowering fellow enthusiasts by sharing her knowledge and experience.