Cycling A Betta Tank

Understanding and performing an aquarium cycle is one of the most important things you can do for your betta. Read on to find out why.

What is cycling?

Cycling is the process of building up beneficial bacteria in your aquarium (mainly in your filter) that help reduce the build-up waste like ammonia and nitrite, which will harm your betta.

Ammonia and nitrite is broken down into less harmful nitrate by these bacteria. The less toxic nitrate can then be removed through water changes. Excess amounts of ammonia or nitrite can kill your betta.

We also go into detail about these bacteria and their relationship with an aquarium filter on our filtration page.
You WILL need an aquarium filter in order to cycle your betta tank.

In order for the 'beneficial bacteria' to arrive we need to add ammonia to the aquarium so the bacteria will first establish itself and grow. Once the bacteria colony is substantially present it can continue to break down ammonia into nitrite. This will then establish the bacteria, which consumes nitrite, breaking it down into the less harmful product, nitrate.

This process doesn't happen over night — patience is key — and we'd argue that understanding the cycle is one of the most important factors when keeping a betta.

Why is cycling so important?

Cycling your aquarium will significantly reduce the chances of your betta becoming ill, providing it with healthy, clean water. It also means water changes will need to be carried out less frequently.

Find more out about betta illnesses here: Betta Disease and Illness

Can't I just cycle my aquarium with my betta in it?

This is what is referred to as 'fish-in' cycling, which can sometimes, more often than not, cause problems for your betta.

We find it to be a rather outdated method of cycling a betta aquarium. It's true that the main source of ammonia build-up in your aquarium will be from your betta's poop and will kick start an un-cycled aquarium. However, having your betta swimming around in ammonia / nitrite without it being broken down can cause your fish to get sick.

If you have no previous experience keeping fish this will most likely happen. We often see newcomers to the hobby finding their betta's beautiful fins damaged from fin rot when attempting 'fish-in' cycling — we want to try to prevent this with the advice in this article.

If you've already purchased your betta and you have not cycled or set up your aquarium and there is no possible way of returning your betta whilst you do so, you may want to check out our Makeshift Betta Tank page.

The method we'll provide on this page is 'fish-less' cycling - which to us should be seen as the only and optimum way of cycling. It allows you to cycle your betta aquarium without adding any fish.

Fish-less cycling is where you add the ammonia to your aquarium in liquid form, which is a much more humane  way than adding a fish and relying on its poop.

What you'll need to cycle your aquarium

  • An ammonia, nitrite, nitrate and pH test kit — we recommend this one on Amazon from API.
  • Conditioned aquarium water. For this you can either leave some water to stand over night so that the chlorine evaporates, or you can use a water conditioner like Aquasafe Plus by Tetra, which you can view here on Amazon.
  • Pure ammonia or ammonia with water
    You can get ammonia or in most hardware stores.

    WARNING: If you purchase ammonia from a store make sure it’s pure ammonia not ‘cleaning ammonia’ which can have soaps, also known as surfactant, mixed in — this is very bad for your aquarium.
  • A good aquarium filter — see our recommendations in our post on the best filters for a betta.

How to cycle your betta aquarium

Before we begin

Test your water parameters / water conditions before cycling your aquarium — to understand what we mean by water parameters, check out our betta fish water conditions page.

Water parameters like pH, heating and hardness preferably need to be checked before you start cycling your aquarium.

Your aquarium should also be fully set up and your filter should be on and running (the filter should never be turned off once on). Again, your aquarium will not cycle without a filter, find out why this is important on our filtration page.

5 steps to cycle your aquarium

1. It may sound contradictory to what we have said above, but we need to first add ammonia to the aquarium to begin the cycle — it provides food for that first batch of nitrifying bacteria that we need to sufficiently populate our filtration.

These bacteria live everywhere, on most surfaces, so they will find their way into the filter. However, without adding a dose of ammonia, a sufficiently sized colony won’t establish itself in the aquarium.

There are 2 sets of bacteria we want to colonise the filter, however only one can occur first. The bacteria that breaks down ammonia into nitrite will be the first to colonise.

We want about 5ppm of ammonia in our aquarium to start. Ppm is an abbreviation for parts per million, which is just a scientific way of saying milligrams per litre. So we want 5 milligrams of ammonia for every litre in the aquarium. To achieve this we must convert milligrams to millilitres.

As an example, let's say our aquarium is 30 litres: 5 (milligrams) x 30 (litres) = 150 milligrams.

To convert milligrams to millilitres we divide by 1000.

150/1000 = 0.15

So 150 milligrams converted to millilitres is 0.15 millilitres.

We therefore want to add 0.150 millilitres of ammonia to our aquarium.

If you've got some standard ammonia from a DIY shop it tends to be mixed with water. This is also known as ammonia hydroxide. It will say if it's ammonia hydroxide or ammonia water on the bottle (please see details above) - A bottle like this usually comes with around 10% pure ammonia to 90% water.

We get our ammonia from a hardware store and it's 10% ammonia and 90% water.

If you have ammonia mixed with water there's just a little extra math to do:

Say you have 10% ammonia to 90% water in your bottle — to add 0.150 ml of ammonia to the aquarium water we need to multiply the percentage of the ammonia in the bottle by the millilitres needed.

10% ammonia — 10 x 0.150 is 1.5 milliliters.

We actually have a ammonia calculator to help you figure this out and want to be certain - just head to

You can use a teaspoon to measure this out. 1.5 millilitres is about a third of a teaspoon, for example. You could also measure this out in a syringe or pipet.

Don’t worry about being super precise, a near enough measure is fine if it goes over a little.

Once you have calculated the correct dosage of ammonia, add it to your aquarium water.

2. It's best to test to see if you have 5ppm of ammonia in your aquarium. We’re using the API Freshwater Aquarium Water Master.

API Freshwater Aquarium Water Master has always been reliable for us and gives accurate results. Instructions on how to test for ammonia etc comes with the kit.

3. Wait for the bacteria to come and eat up the ammonia — test for nitrite in your aquarium water every 24 hours until your have a reading of around 4 - 5ppm of nitrite. This typically takes 4 to 5 days but can take longer.

4. Once you have a reading of 4 - 5ppm of nitrite, you now have food (the nitrite) for the second batch of beneficial bacteria, breaking it down into the less harmful byproduct, nitrate.

At this point the ammonia should now be low or at 0ppm, having been consumed by that first batch of bacteria that established.

Test your nitrate to see if you've got any readings. If you do have readings, the first batch of bacteria is still going to need food (ammonia) in order to sustain itself, so once your ammonia reaches 0ppm be sure to dose the same amount again (unless your nitrate is already giving you values).

Usually at this point you'll still have around 0ppm from nitrate - if this is the case dose the same amount of ammonia again as the first time and wait for your nitrates to read 4 - 5ppm.

5. Once your nitrate is at 4 - 5ppm your aquarium is technically cycled! Just to be sure (if you dosed your ammonia twice) your nitrate should increase over the next 2 - 3 days. If this is the case your aquarium is officially cycled.

It's almost time to add your fish! It’s also a good idea at this point to check your pH again. Your pH may have dropped since you began because the nitrogen cycle does produce acids (nitrite is an acid). Do not worry if your pH has shifted slightly. Once your ammonia reaches 0ppm again do a 50% water change.

Leave your aquarium to run for an extra 48 hours, checking your pH is at an appropriate value every 12 hours.

If so it's time to add your betta!

To understand more about pH check out our page Betta Fish Water Conditions

I've cycled my aquarium but I'm getting odd readings

One of the reasons to go for a 30l aquarium (or above) as recommend by us is that if you're a beginner it reduces the chances of your aquarium parameters ‘spiking'.

Ammonia levels can spike (a sudden high reading) once your fish is in the aquarium if something happens to the beneficial bacteria in your filter. But the higher the volume of the aquarium, the less quickly it will overwhelm your fish, especially if you are ahead of the problem by doing frequent tests of your water.

It also means your aquarium is less likely to overheat or get too cold — see our heating page for more info.

If you've attempted to cycle your aquarium and you’re not getting any nitrate or nitrite readings or your results are varying, that’s when you will need to address other parameters. You may have to adjust other parameters like gH and kH.

You can read more about gH and kH, or what to do if your pH is suddenly spiking or shifting, on our Betta Fish Water Conditions page.

As we recommend at the start of this article — before starting your aquarium cycle it’s always best to check your pH.