How to cycle a fish tank (Without fish and with fish)

It is very important to understand the necessary steps and methods for cycling a fish tank. This process ensures a safe and healthy environment for your fish. If cycling is not done properly, it can negatively affect the health of the fish.

In this guide, I will discuss in detail, based on my experience, how to cycle a new and old fish tank, the various steps involved, and relevant tips to help you create an ideal environment for your fish.

What is Aquarium Cycling?

Aquarium cycling is the process of establishing beneficial bacteria in the tank that support fish health. These bacteria help naturally control harmful chemicals like ammonia, nitrite, and nitrate. This process is very important for the safety of fish and other aquatic animals in the aquarium.

Why is Aquarium Cycling Necessary?

Aquarium cycling is necessary because it creates a stable and healthy environment where fish and other aquatic animals can live safely. In a new aquarium, beneficial bacteria do not exist, but through cycling, these bacteria develop and maintain the chemical balance of the water.

Importance of Aquarium Cycling:

Ammonia Control: Ammonia is produced from fish waste, excess food, and decaying matter. It is very toxic and has a serious effect on the respiratory system and skin of fish. During the cycling process, ammonia is converted to nitrite, which is then converted to nitrate.
Nitrite Control: Nitrite is as toxic as ammonia and interferes with the oxygen-carrying capacity of fish hemoglobin. The cycling process converts nitrite into the less harmful nitrate.
Maintaining Stable Nitrate Levels: Ammonia and nitrite are converted to nitrate through cycling. While nitrate is relatively less harmful, high levels can cause problems for fish. The cycling process keeps nitrate levels within normal limits, which can be further controlled by regular water changes.
Improving Fish Health: When cycling is completed, fish experience less stress, and their immunity increases, resulting in proper growth and bright colors.
Protecting Biodiversity: Cycling creates a stable ecosystem in the aquarium, which also protects aquatic plants, snails, and other inhabitants.
Ease of Aquarium Management: Without cycling, the water quickly becomes polluted, endangering fish and other organisms. The cycling process makes aquarium maintenance easier.

Ideal Cycling Period

Aquarium cycling is the process by which a new or old tank is colonized with bacteria that control ammonia, nitrite, and nitrate. Typically, aquarium cycling takes 4-6 weeks to complete. However, this depends on the method, size of the aquarium, and source of bacteria.

Cycling equipment

Aquarium cycling requires certain supplies and equipment to make the process easy and effective. For example

Aquarium Test Kit: Used to measure the levels of ammonia (NH₃), nitrite (NO₂⁻), and nitrate (NO₃⁻) in the water. Regular testing helps monitor the progress of cycling.
Ammonia Source: Ammonia is needed to start cycling. Ammonia solutions are available at grocery stores for new aquariums (perfume-free). Ammonia can also be produced by the decomposition of food in an aquarium with fish.
Filter: The filter provides the necessary space for bacteria to grow and keeps the water clean. You can use a sponge filter, hang-on-back (HOB) filter, or canister filter.
Aquarium Heater (if necessary): Bacteria grow faster in warm water. Bacteria grow rapidly in warm water, so a heater is needed to increase the water temperature to 24-28°C if necessary.
Oxygen or Air Pump: Ensures sufficient oxygen for bacterial growth and the cycling process.
Water Purifier (Dechlorinator): Chlorine and chloramine inhibit the growth of beneficial bacteria, so a water purifier is necessary.
Decor and Substrate: Substrate (sand or gravel) and decor (rocks, wood, etc.) provide surfaces for bacteria to grow.
Lighting (Optional): If it is a planted tank, lights help with plant growth.

Note: Excessive light can cause algae problems.

Additional Equipment for Regular Maintenance:

Siphon pipe for water changes.
Net and brush for cleaning.
Thermometer for measuring water temperature.

Methods of Cycling an Aquarium

Aquarium cycling can be done in two main ways: 1. Fishless cycling method, and 2. Fish-in cycling method. Additionally, there are some sub-methods: 1. Natural cycling method, and 2. Seeded cycling method. The most popular method among these is the fishless cycling method, which is widely used by aquarium enthusiasts. All methods are explained below:

How to cycle a fish tank (Fishless tank)

The fishless cycling method is a process in which beneficial bacteria in the aquarium are established without using fish. This method is environmentally friendly and completely safe for fish, as they are not exposed to toxic levels of ammonia and nitrite.

Step 1: Set Up the Necessary Equipment for the Aquarium

Aquarium Tank: Choose the right-sized tank based on your preference. Cycling is generally easier in a larger tank, as maintaining a stable chemical balance is simpler.
Filter: A filter keeps the water circulating and provides a habitat for bacteria involved in the nitrogen cycle. You can use a filter that suits your needs, such as a sponge filter, canister filter, or hang-on-back (HOB) filter.
Substrate: Select a substrate based on your fish’s needs, such as sand, gravel, or soil. The substrate supports bacterial growth. If using live plants, opt for a nutrient-rich substrate.
Heater (if necessary): Warm water (25–28°C) promotes the growth of nitrifying bacteria. If the water temperature is lower, use a heater to raise it.
Light: For a planted aquarium, proper lighting is essential as live plants require light. You can use LED or fluorescent lights depending on the plants’ requirements.
Add Decorations: Plants help stabilize the environment quickly, enhance aesthetics, and speed up cycling by absorbing nitrates.

Add Water: Use a dechlorinator to remove chlorine and chloramines from the water before adding it. Pour water slowly over the plate to avoid damaging the substrate or decorations.
. Add the water slowly, pouring it over a plate to prevent disturbing the substrate or decorations.
Turn on the Filter and Heater: Install the necessary equipment in the aquarium. Turn on the filter and, if required, the heater to maintain the correct water temperature.

Step-02: Adding Ammonia

To start the nitrogen cycle for the beneficial bacteria in the aquarium, ammonia must be present in the tank. Since ammonia is not present in a new tank, it must be added.

Created by Organic Matter

A simple and effective way to add ammonia to a new aquarium is to add fish food or other organic matter (decomposable material), as these decompose easily and increase the ammonia level in the tank. If you wish, you can increase the ammonia level by keeping one or two shrimp in the sand of the tank.

Lab-Grade Ammonia

You can increase the ammonia level by buying lab-grade ammonia from the market and adding it to the water. Buy pure lab-grade ammonia from the market. Ammonia that does not have any added fragrances or chemical additives is pure ammonia. Use 0.1 ml of ammonia per liter of water.

Lab-grade ammonia usage method

Add 0.1 ml of ammonia per liter of water. Example: 50 liters × 0.1 = 5 ml. Test the water 30 minutes after adding the ammonia. If the ammonia is between 2-4 ppm, it is ideal. If the level is low, add more ammonia. If it is high, do a partial water change.

Ideal amount

Add ammonia at a level of 2-4 parts per million (ppm) per liter for cycling. If the tank is large (e.g., 100 liters), then add 4-5 ml of ammonia.
Test with an ammonia test kit every day for a week. If the ammonia drops below 2 ppm in a small tank and 3 ppm in a large tank, add organic matter or lab-grade ammonia. Similarly, change the water if the ammonia rises above 4 and 5 ppm.

Step-03: pH Test

pH plays an important role in the cycling process of the aquarium, as the pH level directly affects the efficiency of the bacteria in the nitrogen cycle. A specific pH range is required for the bacteria to function properly and for the nitrogen cycle to be successful.

Ideal pH Range

Nitrifying bacteria (such as Nitrosomonas and Nitrobacter) require a pH of 6.5 to 8.0 to function properly, but the ideal pH value is 7. Bacterial growth may slow or stop if the pH is too low or high. Therefore, if the pH drops below 6.5, the pH should be increased, and if it exceeds 8.0, the pH should be reduced.

Increasing pH

Using crushed coral: Using crushed coral or aragonite substrate gradually increases the pH and carbonate hardness (KH) of the water. This keeps the pH stable in the long term. Add coral substrate directly to the tank. Alternatively, you can place crushed coral in a small bag inside the filter.
Baking Soda Usage: Use baking soda as it quickly raises pH and increases KH. Mix 1/2 teaspoon of baking soda in every 10 liters of water. Mix slowly and test the pH. Do not add too much at once, as it can change the pH quickly, so be careful.
Others: You can increase the pH using dolomite or limestone, KH buffer (e.g., Seachem Alkaline Buffer, API pH Up).

Caution when increasing pH

Change slowly: If the pH changes rapidly, bacteria and fish in the future can be harmed. So, it is better not to change the pH more than 0.2-0.5 per day.
Test the pH: Test the pH regularly using the API Freshwater pH Test Kit or another test kit.
Test the KH (Carbonate Hardness): If the KH is low, the pH can drop quickly. Use baking soda or crushed coral to increase the KH.

How to Lower pH

If the pH is high (8.0 or above) during aquarium cycling, it can affect bacterial activity, and ammonia can become toxic. Lowering the pH is necessary for proper cycling.

Use Driftwood: Driftwood releases tannins into the water, which naturally lowers the pH. Place one or two pieces of driftwood in the aquarium. This will help lower the pH gradually.
Use Catapa Leaves or Indian Almond Leaves: Catapa leaves add tannins to the water and lower the pH, creating a natural environment. Add 1-2 leaves per 20 liters of water. As the leaves decompose, the pH will gradually decrease.
Use Peat Moss: Peat moss lowers the pH and KH (carbonate hardness) of the water. Fill a small bag with peat moss and place it in the filter. This will gradually lower the pH.
Use RO (Reverse Osmosis) water: RO water naturally has a low pH and reduces hardness (GH and KH). Adjust the pH by mixing tap water with RO water. Example: 50% RO water + 50% tap water.
Use CO₂ injection (if planted tank): CO₂ injection lowers pH and is helpful for live plants. Install a CO₂ system. Flow CO₂ at the right level to slowly lower the pH.

Cautions when lowering pH

Change slowly: Rapid pH changes can damage bacteria. Try not to change the pH more than 0.2-0.5 per day.
Check KH (Carbonate Hardness): If the KH is low, the pH can easily drop. To keep it stable, keep the KH between 4-6 degrees.
Test regularly: Test regularly using an API Freshwater pH Test Kit or a digital pH meter.
Avoid excess tannins: Too much tannin can make the water too acidic.

Step 4: Determine the Ideal Nitrite Level

Nitrite (NO₂⁻) plays a key role in the aquarium cycling process, as it is an intermediate step in the nitrogen cycle. The presence of nitrite during the cycling process and its proper management are essential for creating a healthy and stable environment.
Measure nitrite levels every 2-3 days using a reliable test kit (such as the API Nitrite Test Kit). Nitrite levels above 0.5 ppm during cycling are harmful.
Nitrite will temporarily increase during cycling but should gradually decrease to zero. If nitrite is above 0.5-1 ppm, perform a 25-50% water change.

Step 5: Determine the Ideal Nitrate Level

Nitrate (NO₃⁻) plays a key role in the aquarium cycling process, as it is the final step in the cycling process. The presence of nitrate during the cycling process and its proper management are essential for creating a healthy and stable environment.

The formation of nitrate means that ammonia and nitrite have been successfully converted. This indicates that the bacterial colony in the tank is stable. Nitrate is less toxic than nitrite and ammonia. Most fish can tolerate nitrate levels of 20-42 ppm.

If nitrate levels exceed 50 ppm, fish growth, disease resistance, and reproduction can be affected. Use an API Nitrate Test Kit or another reliable test kit to get accurate readings. Perform 30-50% water changes every 1-2 weeks to control nitrate levels.

Step 6: Signs of the End of Cycling

By observing the signs of the end of cycling in an aquarium, you can be sure that the tank is ready for fish or other animals.

After the above steps have been completed correctly, the three main substances in the nitrogen cycle (ammonia, nitrite, and nitrate) are produced and converted during the cycling process. Signs of proper cycling completion are:

Ammonia level at zero: The ammonia level (NH₃/NH₄⁺) has dropped to zero. This is because the bacteria in the tank are able to convert ammonia to nitrite.
Nitrite level at zero: The nitrite (NO₂⁻) level is absolutely zero. By the time cycling is complete, the bacteria are able to convert nitrite to nitrate (NO₃⁻).
Nitrate level rising: The nitrate (NO₃⁻) level is around 20-40 ppm. This is the last step of the nitrogen cycle and the final result of bacterial activity.
Increased water clarity: The water in the tank becomes clear and transparent. This is because the bacterial colonies present during the cycling process have stabilized, making the water appear clear.

Step 7: Fish Release Method After Cycling is Complete

Adding fish after the aquarium has been successfully cycled is a step-by-step process, which is important to maintain the balance of the tank ecosystem. Do not add too many fish at first; start with 2-4 fish, as this is important to avoid over-stressing the ecosystem of the new tank.

Preparing to transport fish: Ensure there is enough oxygen in the bag from the store when transporting the fish and return them home quickly after purchasing to reduce stress.
Acclimatizing the fish to the tank water temperature: Float the bag with the fish in the tank water for 15-25 minutes to acclimatize them to the tank temperature.
Mixing the water: Open the bag and add a little tank water. Wait 5-10 minutes, then gradually add more water. This will help the fish adapt to the pH and other chemical levels of the new water.
Release the fish into the tank: Do not pour water directly from the bag into the tank. Release the fish into the tank using a net. Do not put water from the store bag into your tank, as it can introduce harmful chemicals or pathogens.

Observe the fish’s behavior on the first day: Are the fish swimming normally? Check the tank temperature, pH, and other chemical levels to make sure they are okay. If the fish are lethargic, repeatedly coming to the surface, or hiding, re-examine the tank environment.

Feed less on the first day: Feed very little on the first day as the fish may be stressed by the new environment. Overfeeding can increase ammonia levels, which is harmful to new fish.
Add more fish gradually: Add 2-4 fish at a time. Adding too many fish at once can throw the aquarium ecosystem out of balance. Add new fish every 1-2 weeks and test the tank’s ammonia, nitrite, and nitrate levels.
Continue to test the water: Test the water weekly for the first 2-4 weeks. If ammonia or nitrite levels increase, do a 25-50% water change.

How to cycle a fish tank (Fish in tank)

I do not recommend fish-in cycling because, during this process, the levels of ammonia and nitrite in the aquarium increase significantly, stressing the fish. As a result, the fish’s immunity decreases, making them susceptible to infections. This disrupts their normal life and weakens their overall health.

However, sometimes, due to various circumstances, fish-in cycling becomes unavoidable. In such cases, there is no option but to proceed with the process. The method for fish-in cycling is discussed below.

What is Fish-in Cycling?

Fish-in cycling is a process of aquarium cycling where biological cycling is completed while fish are kept in the aquarium. Through cycling, the levels of ammonia, nitrite, and nitrate in the water are properly controlled. This helps in the growth of beneficial microscopic bacteria in the water, creating a safe environment for the fish.

Step 1: Aquarium Preparation

Aquarium Setup: Clean and set up your aquarium, and properly connect the appropriate filter system and silicone tubing.
Temperature: Maintain the water temperature between 25-28 degrees Celsius.
Turn on the Filter: Start the aquarium filter before beginning the cycling process to ensure proper biofiltration.

Step 2: Fish Selection

Avoid starting with too many fish, as this can cause a spike in ammonia levels, which is harmful to the fish. Begin with one or two small fish, such as guppies, platies, or tetras.

Increase the Number of Fish Gradually: Keep the initial number of fish very small. This allows the ammonia and nitrite levels to increase gradually, giving bacteria enough time to establish themselves.

Step 3: Water Quality and Cleanliness Test

Water Test: Check the ammonia, nitrite, and nitrate levels every 2-3 days. Use an aquarium water test kit to monitor pH, ammonia, nitrite, and nitrate levels.
Water Changes: If ammonia or nitrite levels are excessively high, perform a 25-50% water change every 3-5 days.
Cycling Time: The fish-in cycling process usually takes 4-6 weeks. During this period, ensure the fish are properly cared for to keep them safe.
Do Not Overfeed: Overfeeding can lead to increased ammonia levels. Feed the fish the correct amount daily.

Step 4: Post-cycling Phase

Continue monitoring the health of the fish and the aquarium environment until ammonia and nitrite levels reach zero. Once the levels are zero, the cycling process is complete, and the aquarium will be safe for fish.

Risks of Fish-in Cycling

Fish-in cycling can be risky for the fish. High ammonia or nitrite levels can jeopardize their health and even their lives. It is a stressful process for fish, as they are exposed to contaminated water. Therefore, it is crucial to monitor both the fish and water parameters carefully during the cycling process.

Question and Answer Section

Question 1: What should the ammonia level be?
The ammonia level should be 0 ppm, as it is extremely harmful to fish.

Question 2: How long does cycling take?
Fish-in cycling typically takes 4-6 weeks to complete.

Question 3: What if the fish get sick during cycling?
Immediately perform a 50% water change and start treating the fish.

Question 4: Is fish-in cycling avoidable?
Yes, you can use the fishless cycling method, which is easier and less risky for the fish.

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How to cycle a fish tank