There are dozens of ways to cycle an aquarium and the range of advice and information can seem overwhelming. In this guide I’ll explain what the nitrogen cycle is and how to cycle your tank the easy way.
What is the nitrogen cycle?
Waste is produced by livestock doing “their business” in the tank, rotting plants, uneaten food and any other organic matter that’s left to breakdown in the water. This waste will produce ammonia as it decomposes and since we’re dealing with a closed system, there’s nowhere for it to go. Over time the ammonia will build up to deadly levels.
Thankfully there are some helpful bacteria that love snacking on all that yummy waste and will convert it to a far less toxic form. You will hear people refer to this as nitrifying bacteria, beneficial bacteria or simply BB.
These bacteria break ammonia down into nitrite. Nitrite is still highly toxic to fish, in fact, in many cases it’s more toxic than ammonia. Luckily another strain of beneficial bacteria loves eating nitrite and converts it into nitrate which is far less harmful. We remove nitrate with water changes. Adding live plants will also help because they will consume some of the nitrate.
This process of bacteria converting ammonia to nitrite to nitrate is the nitrogen cycle.
What does it mean to cycle an aquarium?
When we first setup a new aquarium everything is sterile. There is no waste to breakdown and no bacteria present. We need to provide a source of ammonia for the bacteria to feed on, then we need to wait for the bacteria to setup home in our aquarium and begin multiplying.
A tank is considered cycled once it has enough bacteria present to process the amount of waste necessary to keep the water healthy for the fish.
The amount of bacteria required depends upon the amount of waste that it’ll be needing to process. The main factor affecting this will be the amount of food that enters the aquarium.
For either of the methods below, we strongly recommend buying yourself a test kit.
Test strips are very easy to use but be aware that they don't allow you to test for Ammonia. The initial cost of test strips is lower, however you don't get as many tests as you do with a liquid test kit.
Methods of cycling a tank
Fish in cycling:
This method involves adding fish straightaway and performing water changes to keep ammonia and nitrite levels below harmful levels whilst waiting for the cycle to complete. This method is often used by more advanced aquarist and requires a lot of attention. It is not advised for beginners.
This is the method that we’ll be covering in this blog. It is far safer for the fish and will reduce the risk of complications to those just starting out in the hobby.
For this method to work, we need to add a source of waste to the tank and wait for the bacteria to colonise and multiply to large enough levels to break it down. We can add waste in the form of neat ammonia or we can add some food and allow it to breakdown naturally.
My favourite easy method
I recommend simply setting up the aquarium, filling with dechlorinated water, adding any live plants, starting the filter and turning on the heater. Then add a frozen prawn to the aquarium.
After about 4 days you should start to get a reading for ammonia on your test kit. The ammonia levels will gradually build as the prawn breaks down. After another week or 2, nitrite levels should begin to rise and ammonia will start to reduce. Another week or 2 later, you should find that nitrate levels will begin to rise and nitrite will reduce to zero. At this point, your aquarium has enough beneficial bacteria to deal with the amount of waste that a rotting prawn produces. This is roughly equal to a small pinch of fish food once per day. I’d recommend removing the prawn, performing a 50% water change and adding a few fish. Start feeding your new fish very sparingly and keep testing the water to make sure that the cycle is keeping up with the new load. Provided that everything is stable, you’re now able to add a few more fish. Don’t be tempted to suddenly increase feeding because your aquarium is still becoming established and won’t handle sudden large changes in waste at this stage. Gradual changes allow the bacteria a chance to catch up.
This method does require some patience but you’ll be rewarded with a far greater chance of success than if you try to rush things.
There are some products that can speed thing up a bit, such as API Quick Start. This product contains bacteria cysts that will hatch out in your aquarium to help to kick start the colony. I don’t recommend using it as a substitute for fully cycling your aquarium but it can help to speed up the process. Another great method to speed things up is to take some filter media or even a handful of gravel from an established tank. This will be full of beneficial bacteria.
If at any time after adding fish, you find a reading for ammonia or nitrite, I recommend reading this article for help and advice.
Hopefully you found this useful. If you have any questions or comments then please leave them below or contact us for free advice.