How to Cycle an Aquarium

Hey guys,

Welcome to the World of Aquarium. Today I will be partnering with Hurstville Aquarium in Sydney, to run you through how to cycle your fish tank with the nitrogen cycle. This is extremely important as it is maturing your aquarium so you can safely add new fish by first allowing beneficial bacteria to colonise. The nitrogen cycle is constantly at work in nature and we want to replicate that in our aquarium, which is essentially an enclosed ecosystem. Without doing so, you will likely experience elevated fish waste levels that are toxic to the fish and will likely lead to there deaths. 

There are many different ways on cycling your fish tank but I highly recommend the fishless cycle where you establish your aquarium environment before the addition of new fish. The whole cycling process can take several weeks to fully complete and consists of multiple stages. 

The first stage is the introduction of a nitrogen source into your fish tank, as this is needed to feed the beneficial bacteria we will get later on. You can do this by either adding fish food or pure ammonium chloride into your tank water and this is known as ghost feeding. The food you have added will break down over the next few days and gets converted into ammonia, which is the first nitrogen compound of the cycle. 

Your ammonia levels will slowly rise over the week and this will kick off the second stage of your cycle, the appearance of 'Nitrosomonas' bacteria. These are a type of beneficial nitrifying bacteria and their purpose is to convert the toxic ammonia into nitrite. These bacteria will live and grow on all surfaces of your aquarium such as your filter media and substrate. As your ammonia converting bacteria colonies grow, your ammonia levels will slowly decrease but your nitrite levels will start to increase.

This will start the third stage of the cycle, the appearance of nitrobacteria, which is another type of nitrifying bacteria. This bacteria will convert the still currently toxic nitrogen compound, nitrite into nitrate, and this is a lot less toxic to fish. As your nitrite levels gets converted, its levels will slowly decrease but cause your nitrate levels to increase instead. This leads to the final stage of cycling your aquarium which is controlling your nitrate levels. 

Nitrates can still be toxic to fish in high concentrations, so this is why you need to make sure its level isn't too high. The easiest way to control it is by doing water changes as you will be replacing some tank water that is high in nitrates with water that is free of nitrates. Plants will also take nitrate in as fertilizer so they can be beneficial if your tank allows it. When both your ammonia and nitrite levels drop to 0ppm, your tank can be considered cycled and ready for fish. But this doesn't mean you should add all your fish at once as the fish load might be too much for your newly colonised bacteria to deal with. Adding fish should be done slowly over a period of time to allow your tank to adjust for them. Your fish will excrete ammonia waste and this is the nitrogen source that will keep the nitrogen cycle continuously running. 

Please note, that while both types of nitrifying bacteria will appear naturally in your aquarium, they can also be quickly introduced through live nitrifying bacteria products, which are sold in your local aquarium store or by using established filter media if you have some on hand. 

For the first couple months, you should also leave the biological media in your filter alone so you don't disturb the growing beneficial bacteria inside. Afterwards, you can start doing your regular filter maintenance.

I also recommend using test kits to see where your cycle is progressing during this whole process and to measure the amount of ammonia you initially add as you generally want a concentration between 3-4ppm to start your cycle. 

Anyway, this concludes our video on how to cycle your aquarium properly. If you have other questions, please comment below and I will answer them. I hope you liked this video and found it very helpful, thanks for watching.

Please see our video with detail graphs and information on Youtube (https://www.youtube.com/watch?v=QOvD4o0ws_8)

William Zhang (World of Aquariums/Team member @ Hurstville Aquarium)