How Long To Cycle A New Tank

How Long To Cycle A New Tank? Why It’s Important

Fish tank cycling is a very important process that every new fish parent should know about. This is because it matures or it makes fish tank filters capable of continuously eliminating toxic nitrogen waste products from fish tanks.

The elimination of toxic nitrogen waste products from fish tanks is the work of beneficial bacteria. The bacteria breakdown harmful nitrogen waste products into harmless products by feeding them. In order to perform their role effectively, beneficial bacteria need to be grown in a fish tank’s filter system. It is this bacteria growing process that is referred to as fish tank cycling.

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A filter system with adequate beneficial bacteria to continuously breakdown or eliminate toxic nitrogen waste from a fish tank can be referred to as a cycled filter or a mature filter.

Introducing a pet fish into a new fish tank that does not have a cycled filter is not a good idea. This is because such a fish tank will witness a gradual increase in toxic nitrogen waste products that will harm and eventually kill the fish. Therefore, cycling a new fish tank is something that you should do as a responsible fish parent before introducing your pet fish.

You can cycle your fish tank with fish or without fish. Cycling without fish is more humane because it does not expose any fish to toxic nitrogen waste products. 

How long to cycle a new tank?

The amount of time it will take you to cycle a new tank is not set in stone. Since cycling is actually done by bacteria, it is not easy to say how long it will take for you to grow enough beneficial bacteria for your fish tank.

On average a new tank will take between 6 and 8 weeks to cycle.  Smaller tanks under will take less time, 4 weeks or less.  Larger takes may take up to 3 months to cycle.

However, the breakdown of the fishless cycling process below should give you an idea of how long it will take you to cycle a new tank. 

How to Perform the Fishless Cycling Process

  1. Assemble your fish tank completely and add everything but the fish. Everything includes water, a substrate, plants, small rocks, a filtration system, a heater, and an air pump.
  2. Add some fish food to the fish tank. Add no more than what is recommended for the fish you will later introduce. The purpose of adding fish food or fish flakes is for it to decay and start releasing toxic nitrogen waste products. 
  3. Wait. After adding a little fish food to your fish tank, you are supposed to wait. Over the next couple of days, the fish food will start to decay and this will start releasing ammonia and other toxic waste products in the fish tank. 
  4. Start testing for the concentration of ammonia in the water. After waiting for several days (four or five days), you are supposed to start checking the ammonia content of the water in your fish tank. You can scoop a sample of the water and take it to a local fish pet store to have the ammonia concentration tested. Alternatively, you can buy a test kit to test the ammonia concentration yourself. Most aquarium ammonia test kits are very easy to use at home. 

If you test a sample of the fish tank water and find the concentration is equal to or more than 3.0 ppm, you should try to maintain it at that level for a bit of time. The presence of ammonia at 3.0 ppm is an indicator that the fish food you added is decaying well. If the ammonia test reveals that the concentration is below 3.0 ppm, you should add a bit more fish food to the water.

  1. Try to maintain the concentration of ammonia at around 3.0 ppm. This is important. When you test and find that the ammonia level is around 3.0 ppm, you should continue testing the water daily and try to maintain it at that level. 

Maintaining it at around 3.0 ppm is important because once there is this much ammonia in the water, the beneficial bacteria will start to grow and breakdown the ammonia. By adding a bit more fish food to maintain the concentration at around 3.0 ppm, you will trigger the growth of more beneficial bacteria. 

  1. About a week after testing for the concentration of Ammonia in the water for the first time, you should start testing the water for the concentration of nitrites. This is because as the beneficial bacteria begin to grow in the fish tank, they will start breaking down the ammonia into nitrites and other compounds. 

Nitrites are an intermediate compound in the fish tank cycle. They are not as toxic as ammonia to fish but they are still harmful. When you test for them and you detect them, you will know for sure that the cycle has commenced. You are supposed to then continue adding small bits of food to continue feeding the bacteria with decaying organic matter. 

  1. Monitor the water for a sharp drop in the concentration of nitrites. As you continue feeding the bacteria, they will continue growing in numbers. After a couple of days, they will reach sufficient numbers to start converting the nitrites in the water into nitrates. 

This conversion is the final part of the cycle and nitrates are the end product of the cycle. You will know the cycle is complete when the nitrite levels drop below detectable levels or when there is a significant increase in the level of nitrates. 

  1. The cycle is complete. When the nitrites drop to zero, you can introduce your pet fish into the tank as this will be an indication that the cycle is complete and that there are enough beneficial bacteria in the filter system to clear toxic nitrogen waste products from the tank. In other words, the filter or filtration system is mature or cycled.  

As you can see from the steps above, it will take you quite some time and a bit of patience to cycle a new tank. It may take you about four to six weeks depending on various factors such as the size of the tank and the quantity of food you are adding to promote decay and bacteria growth in the tank. 

Although the fish tank cycling process may seem long and tedious, it is important and something you should do if you want your fish pet to live in a safe and healthy environment. 

Sizes of tanks and length of cycle

One thing you have to note is that the bigger the tank, the longer the cycle will be. This is because bigger fish tanks have longer filtration cycles. 

Therefore, it takes longer for decaying organic food to get to the filtration system and it also takes longer for beneficial bacteria to form a colony and start multiplying. So if you have a bigger fish tank, it will most likely take you longer to cycle it.

Seeding the tank

If you do not want to spend a lot of time cycling your new fish tank, you should seed it. Seeding a new tank is like planting bacteria in it. The process is rapidly becoming popular among fish keepers. 

It involves transferring beneficial bacteria from an old or established fish tank to a new one. Introducing this seed (bacterial colony) in a new tank usually halves the amount of time it will take the new tank to cycle.

In other words, if you seed a new tank you will no longer have to wait for four to six weeks to cycle it. You will probably only need two to three weeks.

Methods of speeding up the process

Seeding the tank as explained above is a great way to speed up the fish tank cycling process. Other ways of speeding up the process include adding some substrate from a cycled tank, adding live plants, and adding a pinch of salt to a freshwater aquarium.

Adding some substrate from a cycled tank will speed up the process because the gravel will most likely contain beneficial bacteria if the cycled tank was cycled properly. And the beneficial bacteria will help to quickly establish a big bacterial colony in your new tank’s filtration system. This will obviously speed up the new tank cycling process.

Adding live plants such as Hygrophila and Vallisneria to a new fish tank will also speed up the cycling process. This is because the plants will be continuously absorbing the toxic ammonia from the water for their own biological processes and hence reduce the work of the beneficial bacteria. 

As mentioned, adding a pinch of salt to a new freshwater fish tank will also speed up its cycling process. This is because the salt will reduce the toxicity of nitrites and this will allow you to introduce your fish in the middle of the cycling process as there will be no need for you to wait until the beneficial bacteria break down the nitrites into harmless nitrates. 

So as you can see above, you can speed up the fish tank cycling process in several ways. No need to wait for weeks to get it done.


This article explained the importance of new fish tank cycling. It also explained the different steps of fishless fish tank cycling in a bid to show what is done in each step and how long each step takes. In the later sections of the article, it explained how to speed up the cycling process.