how to cycle a fish tank

Freshwater Fish Tank Cycling: How to Cycle a Fish Tank? (Beginner Friendly Guide)

A fish tank cycling refers to a cycle that is required to activate the nitrogen cycle in aquariums. Going through this process is a must for all the new aquariums. This mechanism helps to establish bacterial colonies and triggers your tank’s nitrogen cycle, thereby making the water safe for fishes to live. The nitrogen cycle or fish tank cycling is a process that involves major three stages, namely, Ammonia, Nitrites, and Nitrates. Cycling a fish tank is not an easy process as it requires time and patience. There is a proper step-by-step procedure, which might take weeks to complete.

This cycle is performed because all living organisms release some amount of waste, and so do the fishes. The waste materials released by your tiny aquarium pets in the water may lead to the generation of ammonia in it, which might, in turn, kill them. However, the cycle helps to release beneficial bacteria in the water that filters it by converting ammonia into nitrites, then into nitrates, thereby making the tank water completely non-toxic for the fishes. Also, if there is too much nitrate in the water, it may allow algae to bloom.

So, you need to check the ammonia and nitrate levels appropriately before putting the fish in the tank water. Here, in this article, we will introduce you to the two ways mentioning its step-by-step procedure for cycling your fish tank. Also, we will highlight the benefits, common issues faced, and test parameters to measure while cycling your aquarium.


What is Meant by Cycling a Fish Tank?

Cycling a fish tank means removing the waste released in the water by the fish. This process is done because the waste hikes up the level of ammonia in the tank water, making it prone to various fish diseases. The beneficial nitrifying bacteria generated in the water during the cycling period will create a safe environment for the fishes by neutralizing their wastes.

The process of cycling your fish tank may take approximately 2-weeks to 2-months. It is a lengthy process, and you will need to have patience with it. Proper monitoring of the cycle is required every other day. Using test kits to check the pH levels of ammonia, nitrite, and nitrates will make the process easy for you.

During the process, you will notice a rise in the levels of ammonia in your fish tank water. The level of ammonia will eventually drop as nitrites start taking hold. Keep in mind that the nitrates will not appear until the nitrite reaches a certain level. When you notice the emergence of nitrates in the water, the level of nitrite will eventually fall, making the water non-toxic. After this, a significant process of cycling will come to an end. When you can see that the water is free from nitrites, you can finally start adding your fish to the aquarium. Make sure that you do not add a lot of fish altogether.


How to Cycle a Fish Tank (Step-by-step Instruction):

As already said before, using two ways, you can cycle your fish tank. One process is that you can cycle your fish tank while having the fish in the aquarium. And the other method is cycling the aquarium without fish in the water. In the forthcoming sections, we will discuss both the ways of fish tank cycling.


Now, let’s start with the first method.

1. Fish Tank Cycling with Fish:

Now, before we start discussing this method, the first thing you should know is that this process should not be your first preference. This method is not suitable for your fish. Fish tank cycling includes the use of a lot of chemicals like nitrite and ammonia, and not all fishes are strong enough to make it through this cycle.

In a case like when you have bought your fish and aquarium on the same day, then out of excitement, you have no option left but to cycle your tank with fishes in it. The bottom line is you must perform this cycle at your own risk.


Step 1: Introduce the fishes in the tank one by one

Adding all your fishes altogether in the water might not be the safest option. It is so because the fishes may end up causing too much waste in the water, which will hike the amount of ammonia to a large extent and may result in the death of your fishes. It takes a while for the beneficial bacteria to grow, so the fish should be hardy enough to survive the high levels of ammonia and nitrite. Some of the hardy fishes are pupfishes, cherries, guppies, minnows, x-ray tetras, etc.


Step 2: Feed

The most common mistake beginners do is that they overfeed their fish. Avoid overfeeding your fish and go by the thumb rule of feeding once every two days. Overfeeding will make the fish release more waste in the water before the generation of beneficial nitrifying bacteria that will help to keep the tank clean. However, indirectly it will increase the waste products in the fish tank, making you clean the tank quite often than usual. Also, the fish will be full and will leave the rest of the food, which will end up intoxicating the water even more severely.


Step 3: Often change the tank water

In this step, you are required to change the water of the fish tank to keep it healthy for your aquatic pets. Water changes in fish tanks are helpful as it prevents the generation of high toxin levels in the water. It is a vital step to manage the balance of ammonia and nitrite in the water. You are required to change 10-25% of the water of the aquarium every 2-3 days. Do not get over-excited while doing this step. If you do it more than this, then you might end up losing all the ammonia and nitrite from the water, which will not form the beneficial bacteria in turn.


Step 4: Testing

In this step, you are required to test the levels of ammonia and nitrite present in the water. Now, testing ammonia is not as vital as testing nitrite, but prefer being on the safer side. Testing nitrite is crucial because it does not appear at first, but rise in your tank eventually. For this step, you’ll need to get testing kits to monitor the toxin levels in the water. Testing is essential because it will allow you to know which elements’ levels fall back or rise in the water. It will keep your fish healthy and in the long run. While it is better if you test your tank daily, if you are busy or lazy, then you can get away with it every 2-3 days.


Step 5: Add more fishes

After performing the whole cycle, your tank will now be free from the toxins, and you can move forward to add more fish in the tank. But, again, be careful and add your fish one by one. Wait for a few days and see how the fishes are coping up. Check the level of nitrite and ammonia in water. Do it slowly; adding too many fishes at the same time will shoot up the toxin levels in the water, causing the fish to fall sick


2. Fish Tank Cycling Without Fish:

Now, this method is quite popular and the most preferred one. The number of views of informative YouTube videos about it, promoted by The Marketing Heaven, speaks volumes in its favour. It is the best and safe because it is a kind procedure that keeps your fish safe.

Step 1: Generation of ammonia

This procedure is usually done using the wastes generated by the fish. But in a fishless cycle, you can add ammonia in the water by adding some fish food to it. Add an adequate amount of food that you would give to your fish. Make sure you are doing it every 12 hours. The food in the water will start to decay, thereby releasing ammonia.


Step 2: Ammonia testing

To test ammonia in the water, you’ll need a testing kit. Perform ammonia testing every day to make sure that the level is not dropping. The level at which you are required to maintain the ammonia is 3ppm (parts per million). If the level of ammonia in the tank water drops below 3ppm, then you must increase it by adding some more fish food in the aquarium and leaving them to decay. Hence, testing is required every other day to maintain the ammonia levels. Once ammonia is released in the water at an appropriate level, Nitrosomonas will grow eventually and start consuming the released ammonia. You need to perform this step for at least a week.


Step 3: Nitrite testing

After a full week of testing ammonia, you are required to test for nitrites. You will need a test kit for this step as well. You will know that the cycle has begun, once you detect nitrites in the tank water. Do not stop adding ammonia, and continue with the process as stated in the previous step.


Step 4: Nitrate testing

After a few weeks of testing nitrites and ammonia, you will notice a drop in the level of nitrite. If you are detecting any nitrate in the water, then you are almost at the end step of the cycle. Once nitrite and ammonia have dropped to zero, you have successfully reached the end of the cycle. If the level of nitrate in the water is above 40, then you will need to make some changes in the water. It is required to drop the level of nitrate in the water.


Step 5: Add your fishes

This step requires much patience. As mentioned above, do not add a clan of fish altogether in the water. Add one or two, and then wait for at least a week. If the fishes seem to cope up with the water conditions well enough, then introduce more. Also, before adding any fish, make sure to use a siphon or hose to clean the substrate, if any. Moreover, the decayed food might be stuck in there, which may release an unwanted amount of ammonia in the tank water.


Common Problems Faced During the Cycle:

The cycling process is not an easy task. While performing fish tank cycling, people come across many issues. However, there are solutions to all these problems. Some of the problems, along with their solutions, are mentioned below:


1. Ammonia poisoning in the fishes:

It can be a significant issue if you are performing the cycle with fish. You may notice some common symptoms like lack of appetite, staying at the bottom, less movement, red streaks in the fins, etc. In such situations, you must take instant action, or it might lead to the death of your fish. Change the tank water to avoid rising ammonia levels. Also, change a greater portion of the water and replace it more frequently.


2. The cycle does not start in the aquarium:

It usually takes the 3rd day for the ammonia cycle to start. However, if you are way past the 3rd day, but you can’t measure any level, then the cycle in your tank has not started yet. Now, a common problem except a faulty test kit, to prevent the start of a cycle in your aquarium might be the presence of a lesser amount of ammonia in the water.

This problem might happen when you are adding fewer sources of ammonia, or there is something in the water that is eating up the ammonia and preventing the bacteria from appearing. So, to prevent this from happening, you can add more ammonia or remove the plants from the aquarium, if any. Wait for a few days and see if there is some change. Test again after a couple of days.


3. No drop in the ammonia level in the fishless cycling method:

If the level of ammonia in the water does not drop, then there can be three reasons behind it. Either you are cleaning it way too much, or performing the cycle in chlorinated water, or the water pH level is too low. You can increase the level by using a pH kit. Also, if you are using chlorinated water, it will end up killing all the bacteria, even the beneficial ones that will prevent the cycle from taking the next step. Do not remove all the decoration or plants in your aquarium, as the bacteria you need, usually live in them. If you clean them way too much, you are keeping the bacteria from establishing.


4. Nitrate level does not rise enough:

If the nitrate level in the water is not raising enough, then it might be due to the presence of something in the water that is preventing the beneficial bacteria from generating. Do not use chlorinated water in your aquarium, as it will prevent the cycle from occurring.


5. Algae bloom:

In this lengthy procedure, you will, unfortunately, face problems like an algae bloom. In such a case, you can try turning off the lights of the aquarium at most times. You will have to make sure that the plants do not get much light, as it will help in blooming algae. Also, do not over-fertilize your aquarium. Injecting carbon dioxide into the water of your fish tank might also help to keep algae away.


Benefits of Cycling a Fishless Tank:

Now, there are several benefits to cycling a fish tank. However, cycling a fishless tank is more beneficial, and some of the significant ones have been listed below.

  • Fishless cycling helps to eliminate potential problems that may be caused due to the introduction of feeder fishes in the tank.
  • In fishless cycling, the risk of the fishes to get prone to any disease gets reduced. It happens because the fish is not exposed to the water with high levels of ammonia.
  • It helps to increase the lifespan of your fish by providing them with a healthy environment in the aquarium.
  • If ammonia is added in high concentration resulting in the completion of the nitrogen cycle, the process helps to keep the fish tank partially stocked.
  • Cycling the fish tank is beneficial for the fish as well as for you. If the aquarium is cleaned adequately, then it will prevent the spread of bad odor in your house. Therefore, it will keep the environment healthy in your home or office as well.


Can We Speed Up the Cycling Time?

Speeding up the process of cycling is difficult, but not impossible by all means. There are a few techniques to quick up the process of cycling your fish tank. In this case, you need to seek help from an established tank. You can adopt the following techniques if you don’t wish to wait for a long 6-8 weeks interval for the completion of the fish tank cycling:

1. Use an established tank filter media:

An established tank will already have nitrifying bacteria attached to its filter media. Thus, it will eliminate the wait for the bacteria to get established in the cycling process naturally, which will, in turn, quicken the first step of the cycle.


2. Use the gravel of an established tank:

A used under gravel filter from an established tank will work the same way as a used filter media. An under gravel filter will have the beneficial bacteria attached to it, which will eliminate the wait for its establishment. Take some gravel and put it in the mesh bag of your filter, or in case of an under gravel filter, place it on the top of your new tank’s gravel.


3. Seasoning of your filter:

In this step, you need to use a new filter, the one that you want to use in your new tank, of course. For a few days, attach the filter to the established tank and let it run with the existing filtration system. This method will allow the bacteria from the established tank to get collected in your new filter. Then, put this newly seasoned filter in your new aquarium, which will release the pre-existing nitrifying bacteria into the water, thereby reducing the cycling time.


4. Add live plants:

You need to use living aquatic plants and not artificial ones for this step. Plants help to generate bacteria and quicken the entire process. The process will be paced more if you use the plants from an established tank. These plants will not only bring beneficial bacteria but also facilitate protein synthesis to balance the level of ammonia in the water.


How to Test the Tank Water Parameters?

Often, people get confused about how to test the tank water parameters effectively. Well, here we will tell you the several ways that you can use to test ammonia and nitrite levels in the tank water.

  • Liquid drops:

Liquid drops are mostly used and highly recommended by aquarists to test your aquarium water parameters. Liquid drops are said to be the most reliable testing kit. The process of using liquid drops is quite simple. You need to add a few drops in some fresh tank water and shake it well. After shaking the water, you will need to wait until the color of the water changes indicating what chemical compounds are present in the water.

  • Test strips:

Using paper strips for testing fish tank water parameters is the most common way. You will get to know about the chemicals present in the water, based on what color the strip changes into. These paper strips change into a variety of colors such as blue or pink, in the presence of different chemicals.

  • Indicators:

There are two types of indicators, namely, automatic and permanent. These testers need to be present in the water as they change color when there is any alteration in the ammonia or nitrite levels. People also tend to get technical while testing tank water by investing in computer-controlled sensors. These sensors measure the levels of ammonia, nitrite, and nitrate and graphically represent them.


What Happens if Fish Tank Cycling is Not Performed?

Even if you do not feel like cycling your fish tank, it will still happen. If you add your fish to the un-cycled water, you will notice that the food and poop of the fish get broken down. It will lead to the introduction of ammonia in the tank water, which is nothing but the first step of the cycle. Now, you will want to remove it, as you will see that your fish are suffering.

Also, the benefit of performing the cycle before adding fish in the water is that you are keeping your fish safe. By not pre-performing this cycle, you will be exposing your fishes to highly toxic water full of ammonia, which might give them a disease or even cause them to die.



Keeping a fish tank requires a lot of care as you are not allowed to feel free once you pre-cycle your aquarium. It is so because the nitrogen cycle never comes to an end. The fish will keep pooping, and the water will become toxic after a certain period. It will require timely cleaning to provide your fish with a safe environment. The process will help to balance the ecosystem in the tank. Therefore, you need to keep a check on the ammonia levels of the fish tank water to keep it safe for your tiny marine pets. So, if you liked our guide on fish tank cycling, comment below and share your experience on setting a fish tank cycle.

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