How to Cycle a New Tank

Starting and cycling your aquarium doesn’t have to be difficult! Understanding how to cycle an aquarium (or pond) is the most important step to maintaining a healthy, underwater ecosystem.

It is vital to differentiate between a “fish in cycle” versus a “fishless cycle”. A “fish in cycle” is the gradual build of the beneficial bacterial colony by leveraging the ammonia naturally produced by the fish. The bacteria will consume the ammonia from the fish waste and respiration to process it from ammonia then to nitrite and finally to nitrate (to learn more regarding the science behind the Nitrogen cycle, see here). Whereas a “fishless cycle” would require daily dosing of ammonia and bacteria to build the bacteria ecosystem prior to fish being acclimated to the aquarium. Both are safe options for fish, but note, this article focuses on the “fish in cycle” process.

To monitor the Nitrogen cycle in the aquarium, the use of an API Master Test Kit for testing the water is key. Your water type will guide you to which kit you would need (Freshwater, Saltwater, Reef or Pond). These kits will provide you with accurate water parameters for your aquarium no matter what type of fish you will be keeping.


Before cycling your tank, you will need to set up the tank with filtration, proper lighting (if applicable), decorations such as gravel and plants, and fill the aquarium with water. Next, you’ll want to add API STRESS COAT™ to dechlorinate the water and API QUICK START™ to quickly seed the tank with nitrifying bacteria to kickstart the Nitrogen Cycle. Once these products applied to the water it is safe to add fish. 

You’ll want to take an initial tank reading for your water parameters before adding fish. The first time testing the water, it will most likely show readings of 0-0.25ppm Ammonia, 0ppm Nitrite and 0ppm Nitrate.

Next, it is recommended to add small amounts of fish at a time (to learn more regarding acclimating fish, see here) during the cycling process. Testing should occur every 3-4 days. You’ll see the fish ammonia start to increase the reading to between 0.5ppm-1ppm. As the ammonia increases, nitrifying bacteria will consume the ammonia and convert it to nitrite. The ammonia reading will lower as it is converted to Nitrite but as Ammonia and Nitrite are both very toxic to fish, it is recommended to do a 30% partial water exchange with the addition of API STRESS COAT and API QUICK START during these elevated readings to help protect your fish but also keeping that cycle moving! The nitrite level will increase and decrease as those nitrifying bacteria convert to Nitrate. You will know when cycling your tank is complete when the readings show 0ppm Ammonia, 0ppm Nitrite and 5ppm-20ppm Nitrate. 

The Nitrogen cycle can take between 2-6 weeks to establish so be patient! Introducing small amounts of fish to your tank, will help keep the ammonia level lower, reduce stress on your fish, and will allow the beneficial bacteria to build quickly. 


The best way to monitor the water parameters and your cycling progress is to track changes using our free AQUASPIN Advise tool here! Testing the water every 3-4 days and documenting the numerical values will allow you to see the progress of the Nitrogen Cycle. 

Its not uncommon for cloudiness to occur during the process, this is an indication of a bacteria bloom. It is recommended to test the water and perform a 30% water exchange if the ammonia or nitrite levels are elevated. 

Once the Nitrogen Cycle has converted the ammonia to nitrite and then to nitrate, you may add a small amount fish to the aquarium. The Nitrogen cycle will start again but will not be as significant as it was in the beginning. Monitoring and documenting the water parameters levels will determine when to perform water exchanges maintenance. Adding API QUICK START to the aquarium with every addition of fish, during water exchanges and on a weekly basis will accelerate the Nitrogen Cycle.

Taking small steps of making sure the water is established, allows for a safe way to kickstart your new tank and your fishkeeping journey. We are here to help you be successful in the aquarium hobby, please reach out with any questions here or use our API Assist interactive helping tool here.

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