Posted on Leave a comment

How to Cycle an Aquarium

How to Cycle an Aquarium

Firstly your aquarium is one of the most important parts of keeping fish and one of the most common questions is “How to cycle an Aquarium so it is safe for my fish ”

The cycling process will ensure that the water in your fish tank is a perfect environment for your fish.

Why do I need to Cycle an Aquarium?

It is important to cycle your aquarium to obtain a correct level of bacteria in your fish tank.

how to cycle an aquarium

What is a Nitrogen Cycle?

To put it simply the nitrogen cycle is to create a process where good bacteria controls the toxic levels within your aquarium.

This is achieved by eliminating bad bacteria such as fish waste and rotting food.

The Nitrogen Cycle is a biological process which involves the continual circulation of nitrogenous compounds, such as ammonia, nitrite, and nitrate to process waste in a natural water environment.

In a closed aquarium, this cycle must be created by your set up in what is commonly called the Nitrogen Cycle.

This cycle is established over time, it can take up to 3 months before a brand new aquarium is fully cycled.

There are certain tricks that can considerably reduce that time.

To create a good aquarium cycle you will need

  • a water filter large enough to cope with the size of your fish tank and the amount of fish you keep.
  • Substrate in the bottom of your aquarium (gravel, plant substrate etc.)
  • An oxygen supply (bubble blower) for oxygenating the water.
  • Heater to maintain a constant temperature.
  • Live Plants are a great choice for an aquarium as they will feed on the waste in the tank reducing bad bacteria.
  • Lighting to replicate night and day for your fish.

Water Filter


Air Pump


Setting up the Cycle

  • Rinse your new aquarium with fresh water do not use any detergents as this can harm your fish.
  • Place your aquarium in your chosen position making sure it is not in direct sunlight.
  • Add your substrate to the bottom of your aquarium making sure it is at least 2 inches deep.
  • Start to fill the tank with water by pouring the water onto a plate so as not to disturb the substrate you can fill to about 6 inches deep.
  • Position any tank decorations and plant live plants into your substrate if you choose to grow plants in your aquarium, also position any bubble blowing ornaments at this point but do not plug them in at this stage.
  • Continue to fill the aquarium to about three quarters full.
  • Position your tank heater and water filter but do not plug them in just yet.
  • Fill aquarium to full usually just below the top band or 3 inches from the top.
  • Add your lighting to the aquarium if you are using under water lighting for effect do this at step five.
  • Switch on your heater, filter, bubble blower and lighting.
  • Make sure everything is working and positioned correctly.
  • Do not add fish at this stage, add some dechlorinator to the water and fish food roughly the amount you would feed your fish this is called ghost feeding, the reason for feeding an empty tank is to start the cycle of waste, filtration and bacteria, continue feeding as if fish were in the tank for at least 4 to 5 days, test the water with a testing kit to see the results.
  • Once you are happy with the water test you can slowly introduce fish to the tank, keep testing the water regularly to see if the readings are ok, if not do a part water change of about 20% to try and neutralize any bad results.
  • When you are happy that the cycle is working increase your fish stock but always check the water regularly and maintain regular 20% water changes.

What to look out for when testing the water

Ammonia, nitrite, and nitrate are the main biological toxins found in a fish tank aquarium, so it is important that the nitrogen cycle works effectively to remove any unwanted waste.

High levels of bad bacteria can be created by over feeding your fish or by overstocking your aquarium, ensure you have a large enough fish tank for the amount of fish you want to keep.

Ammonia, nitrite, and nitrate are the main biological toxins found in the aquarium, so it is important that the nitrogen cycle works effectively to remove these pollutants.

Adding Fish

Stock a new aquarium slowly over time and with younger smaller fish is to allow the nitrogen cycle to develop and keep pace with the gradual increase of waste.

It is natural to want to stock a new aquarium with the prettiest fish and feed them all they seem to want to eat.

However, without the good bacteria which builds up in an aquarium over time, in other words until the aquarium has cycled, the likelihood is many of your pretty fish will die.

Testing your water

Testing Kits

Water testing kits are an important aid for you to monitor your levels they are easy to use and give you piece of mind that your fish tank water is at a safe level.

Water Testing Kit


Testing Strips


Regular part water changes of about 20% will also help you maintain good bacteria levels, don’t do full water changes as this will only mean the process has to start all over again.

Aquarium Light

Lighting your tank is important too much light constantly will create algae, an aquarium light with white light during the day and a blue light at night is the best option for your fish.

Aquarium Lighting substitutes the fishes natural environment lighting out in the wild, a controlled day and night light of white and blue light will replicate the sun during daytime and the moon during the night.

Live Plants

Live plants in an aquarium planted in a good quality substrate will grow very similar to plants you may grow in your garden, Live planting a section of your fish tank will have great benefits.

Live plants help oxygenate the water, but also fish can feed on live plants and use the plants as cover from larger fish, making there environment a very happy place.

I hope you have found this article How to cycle an aquarium useful if you would like to leave a comment below about your techniques or thoughts it would be great to hear from you.

Leave a Reply