How To Know When Your Tank Is Cycled

We all love those beautiful fish tank gurgling sounds of bubbles and how they add to your home’s relaxing effect. However, we also know it requires effort and upkeep to maintain that beauty in a healthy fish environment. For example, not all problems are noticeable to the naked eye, and regularly cycling your tank is a vital process. Cycling a tank is the process of establishing and maintaining a healthy nitrogen cycle in your aquarium. Here are our tips for how to know when your tank is cycled.

Fish tanks are prone to ammonia build-up, which can be detrimental to the fish that live there. So, you keep to all the necessary maintenance activities and have done all the steps to enable water cycling. But how do you know it’s actually cycled? Below, we’re explaining which steps to follow and the different ways to check and confirm the tank cycle process.  

Understanding What A Fish Tank Cycle Is 

It is crucial to understand what the fish tank cycle does so that you can make informed decisions during the process, and can determine when the cycle process is successful. Essentially, it is a process that converts dangerous water toxins into less harmful ones for your fish.

The Nitrogen Cycle has two goals. First, to convert the aquarium water parameters to safe levels that allow fish to thrive and survive. Second, a successful cycle will enable good bacteria to grow and become a biological filter for the waste your fish produce.

Cycling a fish tank is part of the care process for your fish, as they need a healthy habitat to survive. The cycle process can be long but worth the wait in the end. We found this Educational Document that is a bit technical but has valuable information on fish tank cycles, ensuring a healthy environment for your fish.

Initiate The Fish Tank Cycle Process

The first step is to initiate the cycle process, and then allow a few weeks for the cycling process to take effect. After that, the monitoring activities outlined below will provide you with enough information to determine the stage, or completeness, of the cycle. Essentially, we want to create ammonia and turn it into nitrite first. After that, we want to convert the Nitrite to a safer nitrate. Ideally, when you are going through the cycle process, you will not have live fish in the tank.

To speed up the cycle, you can manually add good bacteria to the tank, for example from an existing fish tank, or a bacteria booster. Alternatively, there is a natural method, but it will take longer; below are some examples. 

  • Add a little bit of fish food.
  • Introduce a small fish like a Guppy to start the natural fish-waste process
  • Aquarium plants will increase the ammonia
  • Change 20% of the water at least weekly
How To Know When Your Tank Is Cycled

Test The Water In The Fish Tank

The best, and many believe the only, way to successfully determine the level of nitrates in your fish tank cycle is to test the water. The test kit will produce accurate indicators of ammonia, nitrites, and nitrates levels. Therefore, if you retest every two days and keep a record, you will get a good feel of the process until completion. You can also take a sample of water to your pet store.

You should notice that the ammonia levels will initially rise and lower as the new nitrate bacteria start to get control. After five or six weeks, you should test zero for ammonia and nitrites with deficient nitrate levels. Ensure the nitrates are below 5ppm for saltwater fish tanks and not more than about 20ppm for freshwater tanks. Therefore, these test results would indicate your cycle is complete.

Lastly, the ammonia and nitrite levels in an established cycled tank should always be zero with low nitrate levels. Only then can it be determined that your tank completed a cycle.

Look For Visual Signs In The Fish Tank

Algae can be an excellent visual indicator that the cycle process is working, and it could be very close to the final stage. Again, allow a few weeks for the process to continue. When you see algae forming everywhere, it is a good sign, as many nitrates in the aquarium support algae growth. Continue for another week or two with water changes.

Another visual indicator is to look at and monitor ammonia levels. A continuous high ammonia level will put the fish under stress. Therefore, if the fish do not show signs of ammonia stress, you are well through the cycle process. Some signs of Ammonia stress in fish are: the fish do not eat, they hover at the bottom, or the fish gasp at the surface. Again, this visual monitoring should continue for at least two weeks.

The Steps To Perform A Fish Tank Cycle

  1. Prepare and assemble your new fish tank and plan the tank cycle. You can manually add biological waste while monitoring the water level until process completion.
  1. Remember that this process can be long as you have to wait for the added organic material to start the decay process and produce toxic waste products. 
  1. Next, you can add a few fish flakes, the same amount you would typically add when feeding your fish. However, after a few days, the fish flakes start to decay and produce waste products such as ammonia.
  1. Give it another few days, and then test your water for ammonia. It is crucial to have at least three parts per million. If you do not have the right amount of ammonia, try adding more fish flakes and wait for them to decay a little more in the next few days.
  1. Keep testing your water levels for the right amount of ammonia. As beneficial bacteria produce in your tank, they will slowly take over, and the ammonia levels will decrease. You can add more fish flakes to ensure that the ammonia levels stay at least three parts per million.
  1. Next, you can test for Nitrites as they are the intermediate type of chemical in a nitrate cycle. When you detect nitrites, the process starts.
  1. You will see a sudden drop in nitrites and a slight rise in nitrates. Eventually, enough beneficial bacteria will grow and convert the nitrites into nitrates. 
  1. Monitor until the ammonia and nitrite levels are about zero before gradually adding your fish. After around six to eight weeks, the ammonia and nitrite levels should be undetectable.

How Long Must I Wait Before Adding Fish?

A cautious fishkeeper should wait two to four weeks before adding fish to a brand new aquarium. This comes as a surprise to many people.

In order to keep the water clean and healthy for fish, an aquarium needs a process called the nitrogen cycle to happen. This process breaks down toxic ammonia and nitrite into less harmful substances. The nitrogen cycle takes time to establish and is usually complete in about four weeks. During that time, it’s best not to add any fish so as not to overload the system and cause ammonia and nitrite levels to spike. Once the nitrogen cycle is established, you can add your desired number of fish gradually over a period of several days.

Although you should ideally wait several weeks, you must at a minimum wait 24-48 hours to allow the aquarium to settle. But you should be aware that the lack of a full nitrogen cycle may lead to placing unnecessary stress on your new fish. If you are going to try an expedited route, you should start with a hardy beginner fish that can hold up well under a range of conditions. So, for instance, some mollies would make a good starter fish in these circumstances.

You can also jumpstart the process by adding bottled bacteria or bacteria boosters to your aquarium.

Troubleshooting Fish Tank Cycling Processes

To encourage the growth of bacteria, try to maintain a ph level between 7 and 8. If it is lower than 7, you can add an alkaline such as baking soda. When the water ph level is above 8, add driftwood to help decrease the level.

Install a water heater and keep your water temperature between 70 to 80 degrees. Maintaining your water temperature will allow the bacteria that consume the ammonia and nitrites to grow more comfortably. Of course, if you are in an area with high temperatures, installing a heater is unnecessary. But then, a thermometer can help you regulate the temperature of the water in your tank.

Always ensure that your filter stays clean from algae because if there is too much algae or other substances, it can block the areas where the bacteria need to grow. Therefore, keeping the filters clean regularly is essential.


Cycling your tank is necessary to establish good bacteria in your water; it helps naturally filter your tank and ultimately keeps your fish healthy and happy. You’ll know when your tank has fully cycled when ammonia and nitrite amounts have decreased, and the presence of beneficial nitrates reaches their optimum levels (as determined by testing).

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