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How To Cycle A New Aquarium

Updated on December 4, 2015

What Is Cycling And Why Is It Important?

First of all, if you are not already familiar with the nitrogen cycle, I suggest you do some research as all of this information will make much more sense once you understand the basics of ammonia, nitrites, and nitrates. I've written a hub on water quality and there are many others that will help you if you are interested! As a brief overview, fish excrete wastes that are made up mostly of ammonia. This ammonia can be toxic if it is allowed to build up. However, a well cycled tank will have bacteria that can convert the ammonia to nitrites. Unfortunately, nitrites are toxic as well and require a different kind of bacteria to convert them to nitrates. Nitrates are much less dangerous but still need to be monitored because elevated levels can weaken the immune systems of aquarium inhabitants and can even cause death. Thus, it is extremely important to allow your new tank to cycle and acquire the various kinds of bacteria that allow this process to work.

The Nitrogen Cycle
The Nitrogen Cycle

Add A Few Fish, Or Don't...

The first step in cycling a tank is deciding whether you want to cycle with fish in or out of the tank. If you are setting up a brand new aquarium I suggest holding off on getting the fish and allowing the tank to cycle with no inhabitants. If you already have an aquarium but are setting up a new one, you can get away with having approximately 1 hardy fish per 10 gallons through the cycling process although it is not recommended. Any more than that will overload the new tank and stress the fish. The factor that kick starts the cycle is ammonia. If you are cycling with fish, it will naturally be produced from their waste. If you are cycling without fish, you will need to add fish food that can decompose or commercially bought ammonia additives.

Fish-less Cycle
Fish-less Cycle

Make Sure You Have A Test Kit

The only way to monitor the cycling process is to test the levels of ammonia, nitrites, and nitrates on a regular basis. If you are not familiar with test kits or testing aquarium water I have written a hub on the topic that might be useful. Testing should be done every other day, approximately 12 hours after you add the food/ammonia if you are doing a fish-less cycle. In the beginning you will notice high ammonia levels, obviously. After some time the ammonia levels will begin to drop, while nitrite levels rise. You should continue adding food/ammonia throughout the entire process.

Test Kit
Test Kit

How Long Will This Take?

After approximately 2-4 weeks you will notice that the ammonia and nitrite levels are consistently at zero despite daily additions of food/waste/ammonia. Bacteria (the whole goal of this process) will grow fastest between 77 to 86 degrees. Any higher or lower than this will stunt the growth of the bacteria on the filter. They also prefer a basic pH between 7.5 and 8 and highly oxygenated water. If you can keep your aquarium in these parameters then the cycling process will go much faster.

pH Scale
pH Scale

Once Your Aquarium Is Cycled

Once you aquarium is cycled and your ammonia/nitrite levels are zero and nitrates are low (below 50ppm) you will need to begin adding fish if you haven't already. There must be a constant supply of ammonia in order to maintain the bacteria, so fish should be added on the last day you add ammonia/food. You should only add a few fish at a time, however, to ensure that you don't overload the bacteria either. Continue testing the water regularly in order to determine when/if you should add more fish.

Fully Cycled Tank
Fully Cycled Tank

How Long Did Your Tank Take To Cycle?

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