How to Cycle a Fish Tank or Pond

Nitrogen Cycle
A well established aquarium fish tank with a proper Nitrogen Cycle

How do you cycle a fish tank or a pond? 

In my most recent blog post, I have discussed the importance of the Nitrogen Cycle in aquariums, fish tanks and even ponds. The Nitrogen Cycle is one of the most important processes that keep your fishes and plants happy and alive.

But a very important question was raised in this process. 

How then do you achieve this stability within the setup and get the right amounts of beneficial bacteria ( Nitrobacter and Nitrosomonas) in the waters? 

This post serves as a simplified step-by-step guide to the Nitrogen Cycle and the process known as cycling.

In a brand new environment, there is not enough ammonia to kick-start the nitrogen cycle. For instance, a new fish tank filled with water and aquarium plants, or a newly built pond with water lilies will not have sufficient ammonia present to feed the bacteria present and let them grow in numbers. The basal and low amounts of ammonia present will result in a lack of Nitrosomonas since they have less “food” to eat. This will produce fewer Nitrites as a result. With fewer Nitrites present, there will consequently also be fewer Nitrobacter bacteria present to break down these Nitrites to Nitrates.

Nitrogen Cycle Diagram
A simplified example of the Nitrogen Cycle in Aquariums and Ponds

Step-By-Step Guide to Cycling

Ammonia Production

There will need to be a source of ammonia for the cycle to ramp up in speed and produce sufficient amounts of Nitrobacter and Nitrosomonas bacteria. There are a few ways to go about doing this. One with fish, and one without.

Let’s start with how you can cycle your setup with fish.

Cycling your tank or pond WITH fishes
Step One: Poop is your Best Friend, at least temporarily
Fish Poop and their waste products contains tons and tons of ammonia to initiate the cycling process

Your main goal here is to populate the tank with fish that produce lots and lots of poop. The more waste produced the better. The catch here is that these fish must also be able to withstand the high levels of ammonia and nitrites long enough to allow for the beneficial bacteria to grow and multiply. 

A good guide is to add about 1 to 2 fishes per 10 gallons (or 37.9 litres) of water. Keep in mind that while excess fish will create more waste (good), it can also lead to a sudden ammonia spike and kill off everything (bad).

These fish species should be hardy species that are able to thrive even in a slightly more toxic environment due to the higher levels of ammonia. Fishes such as platies, mollies and mosquitofish are a great start for proper cycling and ammonia production. Try to select those type of inexpensive “feeder fish” as they also tend to be hardier than most species.

Step Two: Feed the Fishes
Feed your hardy fishes sparingly

Feed the fish sparingly, perhaps only a few flakes every now and then. As a general rule of thumb and a good guideline, feed your fish once every 2 days or so.

But why?

Because just like you and me, when fishes have more food. They eat. The more they eat, the more they poop. The more they poop, the more ammonia containing waste matter is being produced. Hence, the higher the level of ammonia, the faster the rate the environment in the water becomes too toxic even for these hardy fish species to handle. 

When the fishes die, your ammonia producers are gone even before the good and beneficial bacteria are able to develop and fully colonize the waters of your aquarium or pond.

Step Three: Sorry, can I get a new glass of water for my fish?
Water Changes should be done once every 2 to 3 days

Since the fishes are being exposed to potentially lethal amounts of ammonia and nitrates, regular water changes are highly recommended. It will help ensure that the levels of ammonia remain at an optimal level to keep the fishes alive while breeding beneficial bacteria.

Aim to do a water change every 2 to 3 days of around 10-30% of the total amount of water. Any more than 30% and you might risk removing excess fish waste and ammonia which the beneficial bacteria needs to feed on and grow.

Step Four: Testing Toxicity

An ammonia test kit such as the API Test KIT Individual Aquarium Water Test Kit can help to detect the levels of ammonia and nitrite in the waters.

By keeping track of the amount in your tank or pond, it will give you a rough idea of how to manage your fishes during the cycling process.

Through testing, you will know when the levels of nitrites drop back down to zero – a universal signal to suggest that the cycling process is finally complete. This suggests that there is now a suitable amount of beneficial bacteria present to breakdown toxic ammonia waste material.

Step Five: More fish for you my friend?
Two Goldfish newly added into a tank environment

Now that the waters are stabilized, feel free to add more fishes into the waters. However, bear in mind that you would have to do this gradually

Yes, I repeat, GRADUALLY

An addition of two to three new fishes every few weeks is recommended. This ensures that the ammonia levels will not rise too quickly beyond the levels suitable for the number of beneficial bacteria present. Adding too many fishes at one go can cause an ammonia spike and lead to nasty algae blooms and even dead fishes.

With that being said, the steps below are the methods to do a fish-less cycle. This is the method that I would recommend you use, for the simple reason that it is HUMANE

Cycling the tank or pond WITHOUT fishes
Step One: Let's get started with Ammonia
Fish Food
Throw a few flakes of fish food or perhaps some crumbs of bread to get the bacteria active

An alternative way of ramping up the amount of ammonia in the tank or pond would be the addition of some food materials into the water. By just dumping a few flakes of fish food, small amounts of bacteria already present will begin to breakdown these food bits into ammonia and other waste materials.

All you have to do now is to wait. Patience is key my friend.

The flakes and food will begin to decay as they are broken down by the small amount of bacteria present – releasing ammonia into the waters of your tank or pond.

You can also add pure ammonia into the tank or pond to get the cycle going. You can get these from your local pet shop or aquarium stores.

Simply add five drops of ammonia per 10 gallons (37.9 litres) of water into the waters on a daily basis. Ammonia levels will rise to three parts per million or 3 ppm.

Step Two: Test the waters for Ammonia

Using an ammonia test kit such as the API Test KIT Individual Aquarium Water Test Kit, monitor the levels of ammonia in your waters every few days. Aim to get the level to at least 3 parts per million (ppm)

If there is still insufficient ammonia after a few days, add more flakes of food or more drops of pure ammonia into the waters.

Try to maintain the levels of ammonia at around 3ppm. At such a concentration, Nitrosomonas will begin to thrive and reproduce rapidly consuming the ammonia. 

Add more flakes of food or drops of pure ammonia each time the levels drop. This ensures that there is always a constant supply of “food” for the beneficial Nitrosomonas bacteria to feed on and thrive.

Continue this process for about a week.

Step Three: Test the waters for Nitrites

Following which, once the week is over. It is time to test for the second compound in the Nitrogen Cycle – Nitrites. Using the API Test KIT I was able to detect accurately the levels of nitrites in the waters. 

The presence of Nitrites in the waters will suggest that the Nitrogen Cycle is finally in full gear. 

Remember to continue adding ammonia as you did before in the form of fish flakes or pure ammonia drops.

Step Four: Test the waters for Nitrates

After a few weeks of testing for both Nitrites and Ammonia, you will want to test for the levels of Nitrates – the final nitrogen-containing compound in the Nitrogen Cycle. 


If you witness the levels of Nitrites decreasing and dropping to lower levels while the levels of Nitrates are increasing, then congratulations, the cycle is nearly completed.

Once you have detected that the levels of Ammonia and Nitrites have returned to absolute zero, the cycle is finally complete. YES! 

This means that the bacteria is present in sufficient amounts to completely breakdown and convert all the toxic ammonia into its less harmful nitrogen-containing form – Nitrates. These Nitrates then can be utilized by the surrounding water plants such as water lilies in ponds and amazon swords in aquariums.

Step Five: Now you can begin adding fishes
Freshwater Fish
A bunch of freshwater fish

It is now safe to add your fishes. Again, I must emphasize that this process should be done GRADUALLY. Don’t go adding bucket loads of fishes in at once. 

Always ensure that you add the fishes gradually to allow for the nitrogen cycle to reboot and adapt to the added amounts of ammonia produced by the new fishes introduced. Should you be too hasty and add in too many fishes at once an ammonia spike could occur, leading to algae blooms and other nasty consequences.

But wait, this all seems too long. Is there a shortcut?

Betta Fish In A Bowl
A Betta Fish in what may be a brand new fish bowl setup

Lucky for you, there is a shortcut! This cycling process of the Nitrogen Cycle can be sped up tremendously using media from an already established tank or pond.

For instance, if you already have a well to do aquarium all you have to do is transfer some of the materials over to your new tank or pond. Water from an already established ecosystem will contain nitrifying bacteria within it. The transfer of water from one established ecosystem to a brand new one will speed up the process of cycling. 

This can be done through the transfer of plants, filter media or even gravel from the old established fish pond or tank. The nitrifying bacteria from your original fish pond or tank will be transferred to the new one you are setting up.

Warning! Warning! Warning!

However, beware that while you may be transferring beneficial bacteria from your old tank setup to your new one, you will also be transferring any unwanted pathogens too! 

So be cautious and NEVER transfer anything from waters that are known to be contaminated and infected with dangerous organisms or disease.

Koi Pond
Transferring of media such as water plants into a new tank setup from a well established pond can speed up the cycling process

Nitrogen Cycling is a necessary part of maintaining a healthy and well-balanced ecosystem in the water. It is unavoidable if you want to have lively thriving fishes and green healthy plants.

Once you have cycled your tank and your levels of ammonia and nitrites are at 0, it doesn’t mean your job is done. The Nitrogen Cycle never ends.

Patience is key my friend, it always is, especially in this case.

Stay happy, First Floor Family. 

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