How to Cycle a Fish Tank the Right Way

How to Cycle a Fish Tank

If you are new to keeping a fish tank or aquarium, you may often hear the phrase, “cycle your tank.” But what is aquarium cycling, and why do you need to cycle a fish tank? More importantly, how do you cycle a fish tank, and is there any way to speed up the process? Let’s learn how to cycle a fish tank.

What is “Aquarium Cycling”?

The term “cycling” refers to establishing a healthy nitrogen cycle inside your aquarium. The nitrogen cycle is a process in natural water where harmful waste is converted into harmless compounds. While this process occurs naturally in wild water, it has to be created in a fish tank.

Without a healthy nitrogen cycle, the natural ammonia and waste that the fish create will slowly make their water more and more toxic and harmful to their health.

Aquarium cycling means establishing a good nitrogen cycle in a new tank, and then maintaining it over time.

How Does a Fish Tank Nitrogen Cycle Work?

Nitrogen is one of the most common elements in the periodic table. In normal conditions, two nitrogen atoms combine to form dinitrogen, an odorless, colorless gas that forms 78% of our atmosphere.

Nitrogen forms extremely strong bonds, which makes it difficult for natural processes to break apart the atoms and convert them into other compounds.

In nature, the nitrogen cycle is a complex process where nitrogen circulates from the air into terrestrial and marine ecosystems, and then back into the atmosphere.

In an aquarium, the nitrogen cycle should follow this path:

  1. Fish eat food and create waste
  2. Fish and food waste is consumed by bacteria and converted into ammonia, a toxic compound
  3. Nitrogen-fixing bacteria consume the ammonia and convert it into nitrite, another toxic compound
  4. Nitrite-loving bacteria consume the nitrite and convert it into nitrate, which is mostly harmless
  5. Very high quantities of nitrate can still be harmful, so the final step in the cycle is:
  6. Living plants consume nitrates and convert them into oxygen and atmospheric gases. Nitrate is also manually removed during regular cleaning and water changes.

As you can see, the nitrogen cycle in an aquarium not only has multiple steps and multiple organisms working together, but it also means having a healthy, balanced ratio of all these elements. For example:

  • An aquarium that has too few fish decreases the number of waste-loving bacteria
  • Too many fish and there may be more waste than the bacteria can consume
  • If an aquarium has no plants, it may become too high in nitrates
  • If an aquarium is cleaned too much, it may harm or reduce the numbers of beneficial bacteria

In other words, all these organisms need to be present and healthy in the right numbers so that they can all work together to naturally keep the water balanced and healthy for the fish. It’s all about developing a balanced, self-sustaining cycle.

Different Ways to Cycle a Fish Tank

There are basically three ways to cycle a fish tank: fish-less, with hardy fish, and with pre-seeding. The key difference between methods is that both ammonia and beneficial bacteria are needed. The different methods reflect where these components come from. Here’s a quick overview of the different cycling methods:

  1. Fishless: Fishless cycling is the best way to set up and cycle a new aquarium because it creates a balanced system that is healthy for fish before fish have to live in the tank. It doesn’t stress fish or risk exposing them to toxic levels of ammonia or nitrites. However, this way of cycling a tank can take a long time, as long as four weeks, and requires you to manually add ammonia to the tank to keep the system active.
  2. Hardy fish: Many people start the nitrogen cycle in their tank with “hardy fish”. These fish are more tolerant of toxic water conditions and naturally create the necessary ammonia. These hardy fish are usually not the species of fish that aquarists want to keep as pets. They often die during the process or are discarded after the cycle is established. Some people feel that this method is unkind to hardy fish, and prefer to avoid it, and it can also take an unpredictable amount of time because different fish produce different amounts of waste.
  3. Aquarium seeding: With this method, you jump-start the nitrogen cycle in a new fish tank by using established bacteria that live in a different, already balanced aquarium. By transferring filter media or gravel from an established tank to a new one, you can transfer the healthy bacteria from one tank to another and shorten the cycling process. This method only works if both the established tank and the new tank have similar water chemistry, so the bacteria can thrive in the new tank. For new aquarists who don’t have access to an established tank with a healthy nitrogen cycle, you can also purchase starter bacteria that shorten the cycling process.

Classic Way to Cycle a Fish Tank

The traditional way to cycle a fish tank is to use the fishless method. This takes time, but helps you make sure that your tank is established and healthy before you add fish. This protects the life and health of your fish, with less risk of death or disease, so most people feel that it’s worth the extra time. To cycle a new freshwater tank using the classic method, you need the following equipment:

  • You will need to have a complete aquarium set up, with lights, heat, and filter, along with your plants, décor, and gravel. The fish tank filter, decorations, and plants provide a home for beneficial bacteria, so they should be in place before you begin.
  • You will also need an aquarium water test kit. Then, test your aquarium water repeatedly during cycling and need very accurate results, so make sure you get a quality kit with enough supplies for many tests.
  • You will also need aquarium ammonia. Use ammonia specifically designed for use in an aquarium because other ammonia products also have additives and unwanted ingredients that will impair your water cycling. Pure aquarium ammonia leaves crystal-clear water with no debris or cloudiness, and is better for the fish.

How to Cycle a Fish Tank

Once you have everything you need, here’s how to cycle a fish tank using the classic, fishless method:

  1. Fill a 5-gallon bucket with water and condition it for use in the aquarium. Allow the water to reach room temperature.
  2. Add three drops of your ammonia product to the bucket and mix it well.
  3. Test the water and review the ammonia levels.
  4. If the ammonia levels are below 5ppm, add another drop of ammonia and mix again.
  5. Test the water again.
  6. Keep adding drops of ammonia until your test reaches 5ppm. Write down how many drops of ammonia you needed to reach 5ppm in a 5-gallon bucket. Multiply that to determine how many drops you need to reach 5ppm ammonia in your fish tank. For example, if it took 4 drops of ammonia to reach 5ppm, and you have a 25 gallon tank, you will need 20 drops of ammonia for your entire fish tank.
  7. Pour the 5ppm ammonia water into your fish tank.
  8. Fill the tank the rest of the way with conditioned water.
  9. Add the number of ammonia drops you need to reach 5ppm in the entire tank and turn on the filter. Keep in mind that you should maintain a pH level of 7 or more, and a temperature of 65-85°F, throughout the cycling process. If needed, adjust your pH levels to 7 to help beneficial bacteria grow more quickly.
  10. After 2-3 days, test your water. Look for ammonia levels and nitrite levels. If you don’t see any nitrites, add enough drops of ammonia to reach 5ppm again.
  11. After 2-3 days, test your water again. If you don’t see any nitrites, top up the ammonia to 5ppm and wait again. This phase of testing and adding ammonia can take up to 12 days. Eventually, when you see reduced levels of ammonia, record the presence of nitrites in your water test.
  12. Once you see nitrites in your water test, reduce the amount of ammonia you add to the water. Every 2-3 days, test the water and add enough ammonia to reach 2-3ppm. This second phase will last 14-20 days of steadily increasing nitrite levels. After 2-3 weeks, your nitrite levels will begin to decline because your nitrite-oxidizing bacteria have begun to work. When your nitrite levels start to decline, reduce your added ammonia down to 1.5-2 ppm.
  13. Continue to text the water every 2-3 days, adding enough ammonia to reach levels below 2ppm, and monitor the decreasing nitrite levels.
  14. After another week or so, your water test should show 0 ppm ammonia and 0 ppm nitrites. The nitrogen cycle is functioning.

How to Cycle a Fish Tank

Getting your cycled tank ready for fish

If you are performing an initial fishless cycle, and your water finally has 0 ammonia and 0 nitrites, you are almost ready to add fish. There are just two more things left to do:

  1. Test your cycle. Add enough ammonia to reach 4ppm. Leave the tank overnight and measure it the next day. Both ammonia and nitrite levels should read 0ppm, with only nitrates in the water. If you still have detectable ammonia or nitrites, the cycle is not complete, so be patient and continue to add drops of ammonia and test.
  2. Perform a water change. If you have 0 ammonia and 0 nitrites, you need to perform a water change to reduce nitrates before adding your fish. Change 60-70% of the water, or as much as needed to get nitrates below 20ppm.
  3. Add your fish! If you aren’t adding fish right away, then continue to add small amounts of ammonia every couple of days to feed your bacteria. Otherwise, you may have to start the cycle all over again.

Fast Way to Cycle a Tank

Classic fishless cycling is the most accurate and humane way to cycle an aquarium because it doesn’t risk any harm to the fish, and manually controlling the amount of ammonia gives you very predictable, accurate results from day to day.

However, it also takes a lot of time, and many people want to see fish happily swimming in their new fish tank sooner.

To cycle an aquarium more quickly, you can purchase an aquarium starter product that already has the living bacteria you need, so you don’t need to wait for them to develop and grow on their own.

When buying an aquarium bacteria starter, here are some things to keep in mind:

  • These bottles should contain living bacteria. Bacteria may die if the bottle has been stored improperly or for long periods of time. Look for a high-quality product, from a reputable source, and choose the freshest bottle you can find.
  • Many of these products claim instant results and that you can have fish in your tank the same day you use the product. That is often an overstatement of how fast and how safe these products are, and it’s better to use caution and stock your tanks slowly, with frequent testing.

Instead, follow these guidelines when using a purchased aquarium bacteria starter:

  1. Fill your aquarium with conditioned, dechlorinatated water.
  2. Turn on your heaters and filters, and keep the water between 65-85°F.
  3. If you have UV lights, keep them off for a couple of days because they can harm bacteria.
  4. Shake your bottle of bacteria well.
  5. Pour it into your aquarium. Some products recommend a certain quantity of product based on aquarium size. However, more beneficial bacteria are always better, and using the whole bottle will jump-start the cycle much more quickly.
  6. Within 2 hours, add one small fish per 10 gallons of water in your fish tank. Do not feed the fish.
  7. Test the water and then feed the fish every other day, and monitor your ammonia levels. If the ammonia is rising to dangerous levels, consider doing a partial water change to reduce them. Otherwise, do nothing.
  8. After two weeks, your ammonia and nitrite levels should be reduced and your nitrate levels should rise. Perform a water change and add a few more fish. Do not completely stock your fish tank all at once; instead, space it out over several weeks and monitor your water quality.

Cycling your aquarium can be tedious and time-consuming, but once you have a healthy balance of fish and bacteria, it is largely self-sustaining. Taking time and care with the cycle makes sure that you have a beautiful aquarium and healthy fish for years to come.