Cycling and how it works...

By: Jbeing75

I see a lot of posts throughout the forum asking what is cycling so this post is for our newer members that have taken the leap into a great hobby and a rewarding one at that. First off I would personally like to say congratulations and thank you for taking the time to talk to members that have years of experience and secondly for doing your research.

So first off what is cycling?
Cycling is the development of bacteria on filter media, glass, decorations, and in the gravel bed. There are two types of bacteria which are needed to successfully cycle your tank. Once these two types of bacteria are developed your tank is effectively capable of holding a specific bioload (amount of fish waste).

How do I know I am cycled?
Once you have begun your initial cycle you will see an ammonia spike. If you are fishless cycling which you should be the ammonia you add will cause the spike. As the nitrifying bacteria are grown you will notice a slight increase in your nitrite levels. As the nitrite builds so will the bacteria that break down the nitrites. After you see your initial nitrite spike your readings on ammonia and nitrite should drop to zero while your nitrates increase substantially as your bacteria starts and ends your cycle. For how to fishless cycle, read the how to section. There is a great article in there by floored I believe.

How does the cycle works?
The chemistry behind the water cycling is this. Oxygen mixes with the growing bacteria and uses the ammonia and nitrites to feed the bacteria and off gas waste.

The first part of the cycle is oxygen mixing with ammonia and feeding the bacteria. The bacteria in turn off gas waste which is nitrites. These bacteria are called Nitrosomonas.
Here is the chemical development of it:

2 NH3 + 3 O2 è 2 HNO2 + 2 H2O

This shows the ammonia and oxygen mixing and developing nitrites.

The second bacteria present are the Nitrobacter or nitrifying bacteria. Both of the bacteria are beneficial bacteria and need O2 to thrive and survive. This is why when fishless cycling it is always better to use an airstone to provide adequate aeration.

2 HNO2 + O2 è 2 HNO3

This is showing the breakdown of nitrites into nitrates. Nitrates are then effectively depleted by plants that use the waste as food or in an unplanted tank water changes.

What happens if I don’t properly cycle my tank?
New Tank Syndrome is the effect of an uncycled tank. The ammonia levels climb much faster than the bacteria can develop and in turn end up causing death to fish by ammonia or nitrite poisoning.

How can I speed up the process of the nitrogen cycle?
Using old filter media from pre-established tanks or pre-establishing a filter on another established tank will increase the nitrogen cycle speed tremendously. You may also use gravel from an established tank as a seeder. The more bacteria you seed in the tank the faster the cycle will go. For example a tank that is brand new with no seeding may take 6 weeks to cycle. A tank with a pre-established filter cycling may take 3 weeks. A tank with pre-established filtration, media, and gravel may take as little as 3-4 days to properly cycle.

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