Cycling The Tank

Once the tank has been filled with water and the return pump and heater set up it is time to establish the tank’s biofilter, more commonly known as cycling the tank.  While products such as Dr Tim's Nitrifying Bacteria can safely cycle a tank in a matter of days, we will discuss how to cycle a tank without using additives. 


Cycling a tank involves the nitrogen cycle and the creation and consumption of three compounds, ammonia, nitrites and nitrates.  At the end of the cycling process the tank will be safe for livestock such as fish and corals. 


The first step of the cycling process involves the creation of ammonia.  While there are commercially available additives, ammonia is also created when fish food breaks down.  This means that all a reefer needs to do is add a small amount of fish food on a daily basis and allow it to decompose in the tank.  This decomposition will create ammonia, the first step in the cycling process.  After roughly a week of adding small amounts of fish food to the tank, use a high quality test kit, such as the Salifert Ammonia Test Kit to verify that the ammonia levels are rising.  Ammonia is incredibly toxic to fish and invertebrates so it is important to resist the urge to add livestock at this point.   


Once the ammonia levels have risen high enough, nitrifying bacteria will begin to consume the ammonia.  This process creates nitrites, which are less harmful to fish, but still dangerous at high concentrations.  At this point, use test kits in order to ensure that ammonia levels are falling and nitrite levels are rising.  Eventually ammonia levels will fall to zero.  At this point the second step of the cycling process is complete.  In the final step, bacteria will begin to consume the nitrites and convert them to nitrates.  Nitrates are a natural part of reef ecosystems and not particularly harmful to fish and can be controlled with water changes.  Once the nitrate levels are rising, and the nitrite levels have fallen to zero, the tank is cycled and is ready for fish and other livestock.  However, at this point it is important to add fish slowly so the biofilter has an opportunity to adjust to the increased bioload. 


While cycling a tank may seem overwhelming it can be summarized in 3 simple stages:


1) Ammonia levels will rise as the added fish food breaks down.

2) Naturally occurring bacteria will convert the ammonia to nitrites

3) The nitrites will then be converted to nitrates and the tank is then ready for fish.


The key to cycling a tank is to take your time and confirm each stage with the use of a high quality test kit.  Your new reef tank will give you many years of enjoyment, so taking a few weeks to properly cycle the tank is well worth the time invested.

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