What is the Nitrogen Cycle?

Breaking in an aquarium or cycling the tank refers to the process of starting the nitrogen cycle in your aquarium. The nitrogen cycle is the process where the toxic compounds generated from fish waste are broken down into non-toxic compounds by beneficial bacteria. Cycling a new tank is very important before you add any fish. Without cycling your aquarium, the fish in your tank will most likely die.

As we have written about in other articles, owning an aquarium is like a living chemistry experiment. It is all about keeping everything in balance to keep the bad things out, and keep the things you want alive and happy.

How Does the Nitrogen Cycle Work?

Many beginner tank owners get confused hearing the terms biological cycle, nitrification process or break-in cycle when it comes to fish tanks. While all of them sound different, these refer to the same thing, the nitrogen cycle. 

In natural water bodies, the fish and other organisms produce waste as poop and urine. This waste releases ammonia that is a toxic compound and harmful to fish. Dead and decaying plant matter or organisms also release ammonia. 

There are beneficial bacteria colonies in nature that convert ammonia into nitrites. There is another beneficial bacteria that feeds on the nitrites and turns them into nitrates. Nitrates are non-toxic and are used as food by plants and algae. This whole process of generating waste and turning it into food for plants is called the nitrogen cycle

The nitrogen cycle is a 3 step process. 

  • In the first step when ammonia is released into the water. Amonia is caused by fish waste, leftover fish food, dead or decaying plant matter in the water. All 3 will break down and trigger a build up of ammonia in the water.
  • Then ammonia is converted into nitrites by a particular type of bacteria. Nitrite is also toxic for fish, just like ammonia is. 
  • In the final step, nitrite is broken down into nitrates by another type of bacteria. Nitrates are non-toxic for fish.

In a new aquarium this process has to be started by cycling the tank. The nitrogen cycle is a continuous process in all fish tanks. It’s what keeps the bad chemicals low and helps the fish thrive. Without a continuous nitrogen cycle, ammonia levels will shoot up and will eventually kill all of your fish.

Why is it Important to Break in a New Aquarium?

Without breaking in or cycling a new fish tank there may not be enough bacteria to efficiently perform the nitrogen cycle. Introducing your fish into the tank could result in a dangerous spike in ammonia levels. High levels of ammonia can burn the gills of your fish or kill them. 

Cycling the tank will keep the ammonia levels at a safe and manageable level. A cycled tank will give you enough bacteria to keep the levels of ammonia and nitrites low and keep your fish happy and healthy.

How Long Does it Take to Cycle a New Tank?

The time this takes all depends on your family’s aquarium size and the method you use. There are two different methods people use to break in a new fish tank. The main factor in why cycling a tank can take a long time is because the beneficial bacteria grows slowly. As we already covered above in the 3 step process, we must wait for 1 step to finish before the next step can begin.

Typically it should take anywhere between 2 weeks to a couple of months for your new tank to cycle. I know how difficult it can be to have a new aquarium at home and not have it full of fish. Please try to be patient during this time and not be tempted to introduce new fish into your aquarium. The tank will be 100% cycled once the level of ammonia, nitrites and nitrites have stabilized. Testing the water quality every few days will let you know when your tank has been cycled.

How to Break-in a New Aquarium?

There are 2 methods that are popularly used to Break-in a New fish tank –

  • Fishless Cycling (easiest and most popular method)
  • Fish-In Cycling

Fishless Cycling

Things You Need 

  • Aquarium Testing Kit
  • 100% pure ammonia
  • Decholrinator

The biggest advantage of this method is that it is done without any fish in the tank. The risk of losing fish due to high ammonia levels is zero. because there is no fish generating waste, ammonia needs to be introduced manually into the tank for the beneficial bacteria to grow. 

Before you begin the process it is important to completely set up your new aquarium. You will need to lay the substrate, and install filter media, heater and add any other equipment you want to use. Then fill the tank with dechlorinated water. Beneficial bacteria need a surface to grow. A sponge filter, substrate, and air pump will give them enough surfaces that they can grow on. The more places the bacteria can grow, the faster the tank can cycle. All the electrical equipment like filters and pumps should be turned on so that it will circulate the water in your aquarium. 

For the tank to cycle fastest, the temperature should be between 65 to 85°F. This is the ideal temperature for beneficial bacteria to grow. Once your aquarium is ready, follow the below steps to cycle your tank.

Check pH of Water

The cycling process can start if the water pH level is above 7. Anything below 7 and the cycling process or the growth of beneficial bacteria will be slow or completely stop. In the United States the pH of tap water is usually greater than 7 so getting above a pH of 7 shouldn’t be a problem. 

The water pH should still be tested regularly with an aquarium testing kit to make sure it is still at or above 7. If during the cycling process the pH drops below 7, perform a 20% water change to increase the pH. 

Adding Ammonia

For the cycling to start ammonia needs to be added into the tank. Because your tank does not have fish waste the ammonia will have to be introduced manually. The easiest way to do this is by adding drops of 100% pure ammonia into the tank. The amount of ammonia you add will differ based on your aquarium size. 

You want to start by adding enough ammonia to bring your aquarium’s ammonia levels to 4 ppm. Assuming that you start with no ammonia in your tank, a 10 gallon aquarium will need 3 drops. A 20 gallon aquarium will need 6 drops. After you add the drops you will want to wait a while for it to dilute into the water before you test.

This is the time that your pumps and filters should be running to help circulate the water around your aquarium. If you don’t have any pumps or filters set up yet you can mix the water carefully using a large spoon. Wait about an hour after adding the ammonia before you test to see what the ammonia ppm levels are. 

Use your ammonia testing kit to see where your water is at. If you are short of 4 ppm, slowly add more to bring it up to 4 ppm. As long as the ammonia is not much higher than 4 ppm, you will be fine if you are a little over. If you go over 5 ppm then you may want to consider doing a 15% water change to lower it. A higher ammonia level can slow down the cycling process.

Make a note of the amount of ammonia you added because you will need it in future. For the next few days keep measuring the level of ammonia with your testing kit. After a week you should see the amount of ammonia in your aquarium dropping as the bacteria starts to feed on it.

Another way, but much slower way of introducing ammonia is by adding fish flakes. The decaying food will release ammonia into the water as they decompose. The main reason this takes longer is because the food will need to start to decay before it will produce any ammonia. You also can’t control the amount of ammonia in your aquarium like you can by just adding drops.

Ammonia Levels Start to Drop

After around a week the ammonia level should start dropping. What this means is that the ammonia eating bacteria has started to grow in your tank. To confirm this you can test the nitrite level in the water. If the nitrite level has increased it means the new bacteria in your aquarium is feeding on the ammonia and converting it into nitrites. 

The new bacteria that has started growing is using ammonia as a food source. If the ammonia level falls to 0 ppm the bacteria will starve and die. If this happens you will have to start the process again. To keep the bacteria thriving, add half the amount of ammonia that you had added before. After adding more ammonia, check the ammonia level to see it is below 5 ppm. 

The nitrite level will keep rising for the next few days until it finally drops. Keep measuring the nitrite levels daily to find out when this happens.

Nitrites Drop

Once you notice the nitrite levels dropping, check for nitrates in your tank. If you get a positive reading for nitrates in your test, it means nitrites feeding bacteria has started growing. 

Continue adding half the amount of ammonia for the next few days and test the water for ammonia, nitrite and nitrate levels daily. The nitrogen cycle will be complete when ammonia and nitrite levels will reduce to 0 ppm within 24 hours of adding more ammonia.

This could take a few days to happen so wait patiently.

To confirm everything is going right, add the amount of ammonia that you first added. Test the water after 24 hours. If the ammonia and nitrite levels are 0 ppm it means your tank has been cycled.

Introduce Your Fish

Your aquarium is cycled now and there is enough bacteria to handle fish waste. Before adding the fish, perform a water change to remove the excess nitrates. Now you can safely introduce fish to your aquarium. 

The waste that the fish will release will now be converted into non-harmful nitrates by the beneficial bacteria. 

If you don’t have the fish yet, continue adding ammonia every day until you finally introduce fish to the tank. Without ammonia the nitrogen cycle will stop and all the bacteria you just created will die. You’ll need to start all over again building it up.

Fish-In Cycling

In fish-in cycling the nitrogen cycle is started by introducing a small number of fish into a new tank. The advantage of this method is that you don’t have to let the tank stay empty for several weeks. With this method you can add the fish just after your aquarium is set up.

Introduce a Few Fish in Your Aquarium

Once your new tank is ready, start by introducing a small number of fish in the tank. The goal is to introduce fish that will generate a small amount of waste and are also hardy. Hardy fish will be able to tolerate higher ammonia and nitrite levels for a short while until beneficial bacteria grow. Some popular hardy fish are:

  • White Clouds
  • Minnows
  • Cherry Barbs
  • Tiger Barbs
  • Zebra Danios
  • Pupfish
  • Guppies

We recommend Zebra Danios (Zebrafish) because they seem to be able to handle just about anything. We recommended adding 1-2 small fish for every 10 gallons of water. Adding more will lead to a large ammonia spike that could kill your fish.

Start Feeding Your Fish

Make sure when you are feeding fish in an aquarium that has not been fully cycled that you don’t overfeed them. Overfeeding them will create extra waste that will cause an ammonia spike. We want ammonia to be released into the aquarium, but without a full cycle we want to keep it as low as we can to avoid killing the new fish. The goal is to have a slow build up of ammonia that will not overwhelm the fish until the bacteria can grow and convert it into nitrates. Only feed them smaller amounts because leftover food will decay and create more toxins.

Do a Water Change

Your fish are in a completely new tank and they are contributing to an ammonia build up. Beneficial bacteria will take a week or two to grow but it’s important to prevent ammonia levels from spiking. Performing 10-25% water changes once or twice a week can help keep the ammonia levels lower. Avoid doing a higher water change because it can disturb the growth of the good bacteria.

Test the Water for Toxin Levels

To understand how and if the tank is cycling, the toxin levels in the water need to be tested. Use your water testing kit to measure the level of ammonia, nitrites and nitrates. Initially you may not find nitrite and nitrates but eventually the level of nitrite will increase.

Test the water every day to see how the level of toxic compounds is changing and continue feeding your fish sparingly. Gradually the level of ammonia and nitrites should drop to 0 ppm. The nitrate level should be just under 40 ppm. Once this has happened, it means the tank has been cycled and your fish can be fed more if you want.

Add More Fish

Your new tank is fully cycled now and you can add more fish. We always recommend a gradual addition of new fish and add only a few fish at a time. After adding new fish wait for a few days and test the water. If ammonia and nitrite levels are 0 ppm it means the beneficial bacteria is doing its job and clearing out the harmful chemicals. 

Avoid adding too many fish at once. Introducing too many fish at once can still lead to ammonia spikes that can stress your fish and cause health issues. 

Ways to Speed up the Cycling Process

There are several ways that can help you speed up the cycling process. These methods involve adding material from an established tank, because an established tank has beneficial bacteria present. Placing the filter or substrate of an established tank into a new tank will speed up the cycling process. It’s important that you don’t try to clean this material before you add it to your aquarium. You won’t have to wait for many weeks for the bacteria to grow because the bacteria was introduced to your aquarium from these items.

Adding living and not artificial plants can also help speed up the process of cycling. Living plants have a large surface for the beneficial bacteria to grow on. One more benefit of adding living plants is that they help remove harmful chemicals in your aquarium. They absorb ammonia from the water to grow.

You can also add live plants from an established tank. These plants can bring helpful bacteria to your new aquarium and also absorb ammonia to continue growing. This is one of the main reasons why we recommend living plants whenever possible.

There are some problems that can be caused by adding filter media or living plants from an established tank. The established tank may have harmful pathogens or bacteria. Introducing things from this tank to a new tank could contaminate the new tank. It is best to avoid transferring anything from a tank unless you know that it’s not contaminated.