The nitrogen cycle, also called the nitrate cycle, is a process that breaks down toxic nitrogen derivatives, originating from fish waste inside the aquarium, into harmless components. For this cycle to develop, the beneficial bacteria that feed on these waste elements must grow within the aquarium's filtration system. It is a bad idea to insert fish without first having done this, because the accumulation of chemical waste inside the water stresses the animals and could kill them. For this reason, the "nitrogen cycle" is a job that should be done every enthusiast when installing a new aquarium, to ensure the health and safety of his fish.
Steps
Part 1 of 4: Activating the Cycle with the Fish
Step 1. Install your aquarium filtration system
To begin, you should completely assemble and set up the tank by filling it with everything you want except fish. You can read the wikiHow articles How to Set Up a Freshwater Aquarium and How to Set Up a Marine Coral Aquarium for more information. Below is a short list of things you need to do before starting; obviously it is a general list and does not perfectly fit all types of aquarium:
- Assemble the aquarium.
- Add the substrate.
- Pour the water.
- Add the air pump, the lava stone and all the accessories.
- Insert the plants, stones and the rest of the "furniture".
- Install a filtration system and / or skimmer.
- Install the heater.
Step 2. Place a small number of hardy fish in the tank
Your goal in this process is to populate the aquarium with a genus of fish that produces waste, but that can survive the rather high initial level of toxins as long as the beneficial bacteria (which break down waste products) they will begin to proliferate. For this reason, choose a species that is well known for these characteristics, but still introduce few specimens. Once the bacteria have grown, you can gradually add more varieties of fish. Here are some species that can trigger the nitrogen cycle:
- White Cloud Mountains Fish.
- Zebra fish.
- Tiger barbel or cherry barbel.
- Maylandia zebra.
- Dwarf gourami.
- Aquatic goldfinch.
- Aphanius fasciatus.
- Most cyprinids.
- Most guppies.
- Note: If in doubt, ask an experienced pet shop clerk for advice.
Step 3. Feed the fish sparingly
When you start the nitrogen cycle of an aquarium with fish in it, it is really very important not to overdo it with food. While each animal species has its own dietary requirements, as a general rule you should feed yours every other day. Offer them only small portion meals; you have to avoid any leftover food left once the fish have eaten. This is critical for two reasons:
- Fish that eat a lot produce a lot of feces, which raises the levels of toxins inside the tank before the colony of bacteria has had time to stabilize.
- Food leftovers eventually rot, becoming toxin producers themselves.
Step 4. Change the water often
While you wait for the nitrogen cycle to complete, try to change around the 10-25% water every 2 or 3 days. Coupled with the reduced diet, such as the one described above, this is another way to ensure that the concentration of toxins does not become excessive before the bacteria have had a chance to develop. If you have set up a marine aquarium, don't forget to add the correct amount of salt every time you change the water, to keep the salinity constant.
- Do not use water containing chlorine; this chemical kills the bacteria inside the aquarium and forces you to start the nitrogen cycle again.
- If, in fish, you notice signs of distress due to ammonia levels, be ready to change the water more frequently (in this regard, read the "Solving Common Problems" section of this article). In any case, avoid putting too much stress on the fish by subjecting them to drastic changes in the chemistry and temperature of the water.
Step 5. Use a kit to monitor toxin levels
When you add fish to the tank, the amount of dangerous chemicals (ammonia and nitrites) rapidly increases as the animals produce feces. Beneficial bacteria develop as a reaction to the presence of these toxins, consequently lowering their concentration almost to cancel it. At this point you can safely add more animals. To control these variations in water chemistry, you can purchase specific kits widely available at aquarium and fish stores. The ideal would be to perform the tests daily, but you can also do it every few days.
- It is recommended to keep the ammonia concentration below 0.5 mg / l and the nitrite concentration below 1 mg / l throughout the cycle (in theory, levels should be around half of these maximum values). If you notice that toxins approach dangerous concentrations, increase the frequency with which you change the water.
- The nitrogen cycle is complete when both ammonia and nitrite levels are so minimal that they become imperceptible. For purely practical purposes, the toxin values are said to be "zero", although this is not technically true.
- Alternatively, you can take a water sample to the shop where you bought the aquarium or fish. Most merchants offer a reasonably priced chemical analysis service (some even for free).
Step 6. Add the other fish gradually, once the harmful chemicals are almost gone
The nitrogen cycle is generally completed in about six to eight weeks. When the ammonia and nitrite concentration is so low that it cannot be detected by the chemical test kit, then you can add other fish to the aquarium, one or two at a time. Gradual supplementation slightly increases the levels of toxins and at the same time the ability of beneficial bacteria to control them.
After introducing a new fish, wait at least a week or so and perform another water test. If the ammonia and nitrites are close to zero, then you can move on to the next fish
Part 2 of 4: Activating the Fish Free Cycle
Step 1. Assemble and prepare the aquarium
For this method, you need to start with a fully set tank, but without the fish, just like in the previous section of the tutorial. However, this time, you will not enter any animals until the nitrogen cycle is complete. You will need to add biowaste manually and monitor toxin levels until the cycle is finished.
You will need a lot of patience, as you will have to wait for the added organic material to rot and start producing toxins. However, it is believed to be a more humane technique, because the fish is avoided exposure to ammonia and nitrites, as is the case with the one described above
Step 2. Add a pinch of fish flake food
At the beginning, a minimum quantity is sufficient, just enough to feed a single specimen. At this point you just have to wait. In the days immediately following, the food begins to rot and release waste products (including ammonia) into the water.
Step 3. Every 2 or 3 days, perform an ammonia test
Use a specific kit or take a water sample to the aquarium shop to check the levels of toxins. You should get a result close to three parts per million (3 ppm). If there is too little ammonia in the water, add more flake food and wait for it to decompose before testing the water again.
Step 4. Try to bring the ammonia concentration to 3 ppm
Continue to check the water every other day. As soon as the beneficial bacteria begin to colonize the tank, they will consume the ammonia, reducing its levels. "Feed them" again by adding more flakes every time the ammonia drops below 3 ppm.
Step 5. After a week, take care of the nitrites
When bacteria begin to consume ammonia, they produce nitrites, an intermediate chemical product in the nitrate cycle (less toxic than ammonia, but still dangerous for fish). Start testing the nitrite levels about a week after starting the aquarium; also in this case, use the home kit or take a sample of water to the fish shop.
When the kit detects the presence of these chemical toxins, then you know for a fact that the cycle has been triggered. At this point, continue to raise ammonia levels as before
Step 6. Wait for the sudden decrease in nitrites and the increase in nitrates
As you "feed" the bacteria in the aquarium with residues that produce ammonia, you will notice that the nitrites will continue to increase. Eventually enough beneficial bacteria will grow to convert the nitrites into nitrates, the final chemical of the nitrate cycle (which is not toxic to fish). When this happens, you can be sure that the cycle is almost complete.
You can detect this final phase by testing the water for nitrites (whose concentration will drop suddenly), for nitrates (whose levels will peak from zero) or for both
Step 7. Put the fish in the water when the ammonia and nitrite concentration is close to zero
After about six or eight weeks, the toxin levels should drop so much that they are not perceived by the tests, while the nitrates should have reached a constant value. At this point it is completely safe to add the animals to the aquarium.
Also in this case, just like in the previous method, it is advisable to gradually add the fish. Do not insert more than two small specimens at a time and wait at least a week or two before placing more
Part 3 of 4: Accelerate the Process
Step 1. Add a filter medium from a “mature” aquarium
Given that the nitrogen cycle can take six to eight weeks, many aquarium enthusiasts have found "shortcuts" to speed up the time. A verified technique is to introduce the bacteria that have developed in another tank. Since you don't have to wait for the bacteria to start growing naturally, the nitrogen cycle will be much faster. An excellent source of bacteria is the aquarium filter. Simply move the filter medium from the "old" aquarium to the new one to achieve the desired results.
Try to use an aquarium filter that is similar to the new one in size and number of fish. If you are using unsuitable filters (such as a sparsely populated aquarium for a tank that will hold many animals), then you may face a substantial increase in ammonia levels that the bacteria are unable to process properly
Step 2. Add gravel from a mature aquarium
Exactly as happens with the change of the filter, this is also a method to "transfer" the bacteria from a stabilized tank to a new one thanks to the substrate (the gravel on the bottom, in fact). Simply add a couple of spoonfuls of "used" substrate to your aquarium to reap the benefits.
Step 3. Insert live plants
Real ones, unlike plastic ones, usually accelerate the nitrogen cycle, especially if they were taken from a mature aquarium. Not only do plants carry beneficial bacteria (just like gravel and filter), but they also eliminate ammonia from the water, thanks to their natural metabolic process called protein synthesis.
Plants belonging to the fast-growing varieties (for example vallisneria and hygrophila) tend to absorb most of the ammonia. Floating plants are usually fine
Step 4. Be very careful of the risks of cross contamination
One of the disadvantages of using the filter medium or substrate from another aquarium to inoculate the good bacteria into the new tank is that other organisms can be transferred. In this way, many parasites, invertebrates and microorganisms can also be introduced, so be aware of this risk and never use material from an aquarium that you know is contaminated.
The parasites that can spread are snails, dangerous algae and parasites such as Ichthyophthirius multifiliis, responsible for ichthyophtyriasis, and ooodinium
Step 5. Add small amounts of salt to fresh water tanks as well
If you have set up a freshwater aquarium, a little salt helps the fish stay healthy even when the toxin levels are high, at the beginning of the nitrogen cycle. This works because it reduces the toxicity of nitrite, the intermediate product of the nitrate cycle. However, you must use a maximum of 12 g of salt per 4 liters of water, a higher concentration could stress freshwater animals.
Be sure to use certified aquarium salt, table salt is unsuitable and could harm fish
Part 4 of 4: Solving Common Problems
Step 1. Treat ammonia suffering in fish with frequent water changes
Stress caused by ammonia (a series of dangerous symptoms that fish manifest when the concentration of this toxin is too high) is always a risk during the nitrogen cycle. If not dealt with quickly, the symptoms become fatal to the animals. If you notice the signs described here, you absolutely must reduce the ammonia levels by changing the water more frequently and in larger quantities:
- Lethargy or lack of movement even when food is given.
- The fish does not leave the bottom of the tank.
- The fish gasps on the surface.
- The eyes, gills or anus of the animal are inflamed.
Step 2. Consider using an ammonia neutralizer if you notice toxicity problems
Most pet shops and aquariums sell chemicals specially formulated to neutralize ammonia. Although they are very useful for controlling ammonia concentration and preventing it from becoming dangerous for fish, there are still doubts that they are more effective than a water change.
There is also evidence that these neutralizers are toxic in the long run. In fact, they only convert ammonia into a form that is not dangerous for animals, while preventing beneficial bacteria from drawing nourishment and colonizing the tank. The bacteria will die and the ammonia emitted from the fish feces will begin to accumulate again with the need to subject the aquarium to a new cycle
Step 3. Use goldfish to start a nitrogen cycle only if you expect that the aquarium will only contain these animals
Although this animal is thought of as the classic aquarium fish, it is not actually recommended for triggering a cycle in the tank. The problem lies in the fact that goldfish needs special and different care compared to other tropical fish which are more common among aquarium enthusiasts. Therefore, starting a tank with goldfish and then letting us live other varieties of animals causes, at the very least, the death of some beneficial bacteria due to the increase in temperature and different water conditions. All of this causes stress for goldfish, bacteria and tropical fish, and is not exactly ideal for a healthy aquarium.
- Additionally, modern goldfish are somewhat susceptible to diseases that can spread throughout the tank.
- We strongly advise against starting the cycle of "any" aquarium with goldfish bred to become "bait". These are raised and kept in poor condition, by both nurserymen and retailers, and are particularly prone to disease.
