How to Create a Nitrogen Cycle in an Aquarium

The nitrogen cycle (also called the nitrification cycle) is a process that breaks down toxic nitrogen waste in the aquarium into less toxic components. To create a nitrogen cycle, the beneficial bacteria that consume waste need to be grown in the aquarium’s filtration system. It’s not a good idea to put fish in a tank that hasn’t been cycled – the chemicals in the waste can cause serious stress to fish, and even kill them. Therefore, anyone installing a new aquarium needs to create a nitrogen cycle to ensure the health and safety of the fish. ^{[1] X Research Source}

Table of Contents

Creating a nitrogen cycle with fish

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Install fish tank and filtration system. To start creating a nitrogen cycle, you need to completely set up the aquarium and put in it everything you like along with the fish. You can read our article on how to install freshwater and saltwater aquariums for more information. Here’s a list of things you need to do before you get started; This list may not be completely suitable for every aquarium:

Install fish tank
Lining background material
Put water in the tank
Add pumice, pumps, etc.
Add plants, rocks, etc…
Install filter system (and/or protein skimmer)
Install the heater

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Put some easy-to-grow fish into the tank. The purpose of the nitrogen cycle is to release fish into the tank to create waste, but the fish must be able to survive in water with high levels of toxins long enough for waste-processing bacteria to thrive. As such, you need to choose fish species with good microbiological potential, and start with only a few. Then, as the bacteria have grown, you can gradually add other fish species. Here are some suitable fish species: ^{[2] X Research Source}

White Clouds
Zebra fish (Zebra Danios)
Tiger Barbs (Tiger Barbs)
Blue striped Ali fish (Pseudotrophius Zebras)
Banded Gouramis (Banded Gouramis)
X-ray Tetras (X-ray Tetras)
Pupfish
Most minnows (minnows)
Most varieties of guppies

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Feed the fish less. When creating a nitrogen cycle in an aquarium, it is important that you do not overfeed your fish. Although different types of fish have different nutritional needs, a general rule of thumb is to feed fish only once every two days , in a moderate amount each time; Do not leave food left over when the fish is done eating. There are two reasons to do so:

Fish that eat a lot will excrete a lot of waste, causing the level of toxins in the tank to rise before the bacteria are able to stabilize.
Leftovers will rot and also produce toxins.

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Change water regularly. While waiting to create a nitrogen cycle in the aquarium, every few days you need to change about 10-25% of the water in the tank. Similar to the reduced feeding schedule above, water changes are also a way to ensure toxin levels don’t get too high before bacteria are likely to grow. If it is a saltwater aquarium, don’t forget to add salt mixed with sea water in the correct proportions during each water change to maintain the proper salinity.

Do not use chlorinated water because chlorine can kill bacteria in the tank, and the nitrogen cycle will have to start all over again. If using tap water, be sure to treat it with an appropriate dechlorinator or water treatment agent before adding it to the tank. If using bottled water, use distilled water, as “pure” or “drinking” water can contain flavor minerals that are harmful to fish.
Change the water more often if you begin to notice signs of severe ammonia stress in your fish (see more information in the “Treating Common Problems” section below). However, you should try not to stress the fish by avoiding large changes in temperature and chemicals in the water.

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Use the test kit to monitor toxin levels. When fish are added to the tank, the levels of toxic chemicals such as ammonia and nitrites will increase rapidly in the water. As beneficial bacteria begin to grow and react to these chemicals, toxin levels will drop to near “zero” – a safe level for stocking more fish. To monitor these chemicals, you can use a test kit commonly available at aquarium and aquarium stores. Daily water testing is ideal, but sometimes you can also test the water every few days.

You also need to keep ammonia below 0.5 mg/L and nitrite below 1 mg/L throughout the cycle (preferably less than half of the numbers above). If these chemicals start to rise to unsafe levels, you need to increase the frequency of water changes.
The nitrogen generation cycle is complete when both ammonia and nitrite drop to undetectable levels. In practice, this level is often referred to as a “zero” level, although technically incorrect.
You can also take a water sample to the store where you bought your fish or aquarium. Most of these places offer low-cost water testing (some are even free!) ^{[3] X Research Source}

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Gradually release more fish as the toxin level drops to close to “zero”. The nitrogen cycle usually takes about six to eight weeks. You can add more fish when the ammonia and nitrite drop to undetectable levels with the water test kit. However, you need to do it slowly, releasing only one or two new fish at a time. Drop a few fish at a time so that the ammonia and nitrite levels in the water only increase to a level that the bacteria can control.

After each addition of fish, you need to wait at least about a week and test the water again. If the ammonia and nitrite levels are still low, you can add a few more fish.

Create a nitrogen cycle in a “fish-free” tank

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Install and prepare the aquarium. With this method, we will start with a fully installed aquarium like the method above, but this time do not release the fish until the entire nitrogen cycle is complete. Instead of stocking fish, we will give microbiological waste, while monitoring the water level and waiting for the cycle to complete.

You have to be very patient, as this method requires you to wait for the organic matter in the aquarium to rot and start creating toxic waste. However, this is the option that is generally considered to be more “humane” because it does not expose the fish to an ammonia and nitrite environment like the above method. ^{[4] X Research Sources}

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Sprinkle the aquarium with some flake food. To start the nitrogen cycle, add the same amount of flake food as you would normally feed your fish. Now you just have to wait. A few days later, the food particles begin to rot and release toxins (including ammonia) into the water.

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Test ammonia levels after a few days. Use a test kit (or take a water sample to the aquarium store) to test the ammonia level. The ammonia level should be at least three parts per million (ppm) . If the amount of ammonia in the water is not reached, you need to add more fish food and wait for it to rot before trying again.

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Try to keep ammonia levels around 3 ppm. Continue measuring ammonia levels every 2 days. When beneficial bacteria begin to grow in the aquarium, they will begin to consume ammonia, helping to reduce ammonia levels in the water. Make up for it by adding fish food every time the ammonia level drops below 3 ppm.

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Start testing nitrite levels after a week. Once the bacteria start consuming ammonia, they begin to release nitrite, a chemical intermediate in the nitrification cycle (less toxic than ammonia, but still harmful to fish). Start testing nitrite levels after a week; As above, you can use a test kit or take a water sample to the aquarium store to do this.

When nitrite is detected in the water, the cycle has begun. At this point, you need to continue to increase the amount of ammonia equal to the previous level.

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Wait for the nitrite level to drop suddenly and the nitrate level to rise. When you feed the bacteria in your tank with ammonia, the nitrite levels continue to rise. However, over time, beneficial bacteria will grow enough to convert nitrite to nitrate , the final chemical in the nitrification cycle (and not harmful to the fish). When this happens, you’ll know the cycle is almost done.

You can identify this last stage in the cycle by testing the nitrite level (in which case you will observe a sudden drop in nitrite), the nitrate level (in which case you need to look for a nitrate spike from level “zero”), or both.

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Gradually release the fish into the tank as the ammonia and nitrite levels near zero. After six to eight weeks, the ammonia and nitrite will drop to levels you can no longer measure, while nitrate levels will stop. It is safe to release fish at this time. ^{[5] X Research Sources}

However, like the method above, you need to release the fish gradually. Do not stock more than a few fish at a time and wait at least a week or two before releasing the next batch of fish.
Consider cleaning the aquarium substrate with a siphon before adding more fish to the tank, especially if you have to feed a lot. Rotten food or organic matter can become a ticking time bomb. If organic debris gets trapped underneath the gravel, the ammonia won’t get into the water, but if disturbed, large amounts of ammonia can escape fairly quickly.

Accelerate nitrogen cycle generation

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Use filter media from an aquarium that has completed the nitrogen cycle. Since nitrogen cycling can take 6 to 8 weeks, many aquarists are constantly looking for ways to shorten the process. One way that is widely believed to be effective is to introduce bacteria from a nitrogen cycled aquarium into a new tank. Since it doesn’t have to wait for bacteria to start growing naturally, your aquarium will complete the cycle faster. A very good source of bacteria is the aquarium filter; you just need to change the filter media from the stabilized aquarium to the new one to speed up the cycle.

Try to find filter media from an aquarium of the same size and number of fish. Incompatible filters (such as if you use a filter for an aquarium with only a few fish for an aquarium with more fish) can result in more ammonia build up than bacteria can handle. timely.

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Add gravel from an aquarium that has completed the nitrogen cycle. Just as filter media can help you “inoculate” bacteria from an established aquarium to a new one, the substrate (the gravel layer on the bottom of the tank) of a nitrogen cycled aquarium can have an effect. similar. All you need to do is spread a handful of gravel over the base of the new aquarium.

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Planting plants in the aquarium. Aquatic plants (as opposed to fake plastic plants) often help speed up the nitrogen cycle, especially when taken from a stabilized aquarium. Aquatic plants not only carry beneficial bacteria (similar to the substrate material mentioned above), but also directly absorb ammonia in a biological process called protein biosynthesis.

Fast-growing species (e.g. Vallisneria and Hygrophila) are usually the most able to absorb amino acids. Plants floating on the water also have a good effect.

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Beware of cross contamination. One downside to using a filter block or substrate to transfer probiotics from one tank to another is the potential for other organisms to be accidentally transferred as well. Many species of parasites, invertebrates, and mixed microorganisms can be spread this way, so be aware of this possibility in advance and never use materials from a used aquarium. harmful organisms.

Pests that can be transmitted this way include snails, harmful algae, and parasites such as ich and velvet.

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Add a small amount of salt to a freshwater aquarium. For freshwater aquariums, you can add a very small pinch of salt to keep fish healthy when toxins are at their highest at the start of the nitrogen cycle. This has the effect of reducing the toxicity of nitrite, a chemical intermediate in the nitrification cycle. However, you should only use a maximum of about 12g of salt per 4 liters of water. Higher amounts of salt can cause severe stress for freshwater fish.

Make sure to use standard aquarium salt; Formulated table salt is not suitable for aquariums and can be harmful to fish.

Handling common problems

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Deal with ammonia stress in the nitrogen cycle with regular water changes. Ammonia stress (a dangerous symptom that occurs in fish when ammonia levels get too high) is always a risk in the nitrogen cycle. If not treated early, these symptoms can eventually kill the fish. If you notice any of the following symptoms in your fish, you need to lower your ammonia levels by changing the water more often and with more water each time: ^{[6] X Research Source}

Lethargy/less movement (even with food in the aquarium)
Refusing to leave the bottom of the tank
Take in the air above the water
Inflammation of the eyes, gills and/or anus

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Consider using an ammonia neutralizer if toxicity-related problems occur. These products are of two types: ammonia reducers and detoxifiers. Most aquarium stores sell chemicals specifically designed to remove ammonia in aquariums. These chemicals can help when ammonia levels get so high that they start to harm the fish, but they’ll be even more useful when starting a new aquarium installation, as you can then skip a few changes. water, shortening the nitrogen cycle time for the new aquarium.

Some people argue that ammonia reducers can be harmful in the long run. ^{[7] X Source of Research} This perception may stem from a misunderstanding of the detoxification process. Toxic ammonia (NH3 gas) is in reversible equilibrium with less toxic ionized ammonia (NH4+). Most detox products convert toxic ammonia into a form that is not much toxic to fish. However, the ammonia will come out after a period of 24 – 48 hours. That’s why these products should be used as follows:
- continue to use as long as beneficial bacteria have not stabilized, AND
- occasionally used during partial water changes (following individual manufacturer’s instructions) to remove some ammonia build-up ^{[8] X Research Source} , AND
- Even if it’s not well defined, it’s still a good idea to dose the disinfectant for the entire aquarium and not just for the new water, as the ammonia that’s stuck in the aquarium will soon be released (after 24-48 hours from the date of delivery). previous dose).
When you do a 50% water change (or more), the time it takes to cycle the nitrogen gets longer (or even stops the cycle) because the beneficial bacteria are temporarily inhibited and it takes time to acclimate. acclimatized to the new pH. ^{[9] X Research Source Book: “Nitrification and Denitrification in the Activated Sludge Process”/Michael H. Gerardi} . For this reason, some people recommend that the pH change be less than 0.2-0.3 per day. Assuming the pH in the tank is 7.8, when changing 25% of the water with pH = 7, the final pH will be 7.6.
Beneficial bacteria only convert ammonia to an ionized (non-toxic) form, so these products are also beneficial for bacteria. ^{[10] X Research source} .

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Only use goldfish to create a nitrogen cycle for a tank full of goldfish. Although often considered a typical aquarium fish, goldfish are not actually recommended for use in the nitrogen cycle of aquariums. This is because goldfish have different care needs than popular tropical ornamental fish today. So, using goldfish to cycle the tank’s nitrogen and then stocking tropical fish can cause at least some bacteria to die due to higher temperatures and different water environments. ^{[11] X Research Source} This will stress goldfish, bacteria and tropical fish; therefore this is not the way to maintain a good environment in the aquarium.

In addition, new species of goldfish can be susceptible to diseases that can spread to the entire aquarium. ^{[12] X Research Source}
You should not cycle the nitrogen in every aquarium with the so-called “bait” goldfish, which are not well cared for by breeders and sellers and are often susceptible to disease. ^{[13] X Research Source}

Advice

Pure ammonia can also be used to cycle nitrogen in fish-free tanks. Use only pure ammonia with no other additives. You can calculate the dose to add to the tank by searching the keyword “ammonia spreadsheet”.
Don’t hesitate to speak with a professional if you have questions regarding your aquarium. Better safe than sorry! However, you should also keep in mind that many aquarium stores do not hire professionals.
Another way to speed up the nitrogen cycle is to use a bacterial supplement. Most aquarium stores sell cultured bacteria, so if you don’t mind spending a little extra you don’t have to wait 6 weeks to complete the nitrogen cycle. However, some people claim that the bacteria in these products are ineffective, so you should still “test” the bacteria for ammonia.

Warning

A nitrate level exceeding 40 ppm and ammonia/nitrite exceeding 4 ppm means that you need to adjust the water slightly, as this can be detrimental to the healthy bacteria you are growing.
Using large pieces of food or organic matter to cycle nitrogen (excrete ammonia) can cause bacteria to thrive and cause unpleasant odors. Food can also become moldy underwater, causing disease in fish and creating conditions for mold growth in the substrate.

Steps