Starting the Biological Cycle in your Aquarium

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The Biological Cycle or Nitrogen Cycle

You must exercise patience when setting up a new freshwater tropical aquarium. It takes time for nature’s biological process to begin working in your aquarium… usually a minimum of 4 to 6 weeks.

Here’s an explanation of the Biological Process

The biological cycle depends on beneficial bacteria to break down toxic organic compounds into less toxic compounds. We can then safely manage these less toxic compounds through weekly water changes. The beneficial bacteria that we need to culture in the aquarium is called Nitrosomonas and Nitrobacter bacteria.

Nitrosomonas bacteria breaks down deadly ammonia to less toxic nitrite. Nitrobacter bacteria then converts nitrite to an even less toxic nitrate. You can’t see these toxic chemicals in the aquarium, they can only be detected with test kits. Sometimes algae blooms are an indication of excessive nitrates.

Why is Biological Cycle (Nitrogen Cycle) Important?

  1. Nitrogen Cycle: The primary reason for cycling is to establish the nitrogen cycle in the aquarium. The nitrogen cycle involves the conversion of toxic ammonia, produced by fish waste and decaying organic matter, into nitrite and then into less harmful nitrate. This process is facilitated by beneficial bacteria.
  2. Beneficial Bacteria Colonization: Cycling allows for the growth and colonization of beneficial bacteria in the filter media and substrate. These bacteria play a critical role in breaking down and converting harmful substances, ensuring a safe and stable environment for fish.
  3. Ammonia and Nitrite Detoxification: Ammonia and nitrite are highly toxic to fish and can lead to stress, illness, or even death. The establishment of a mature bacterial colony during cycling helps detoxify these substances, making the aquarium safe for fish.
  4. Stabilizing Water Parameters: Cycling helps stabilize important water parameters, including pH and hardness. Sudden changes in these parameters can stress fish, and a stable environment is essential for their overall well-being.
  5. Preventing New Tank Syndrome: New Tank Syndrome refers to the challenges and risks associated with setting up a new aquarium without a properly cycled system. Without established beneficial bacteria, ammonia and nitrite levels can spike, posing a significant threat to the health of the fish.
Nitrogen Cycle

How do I start the Biological Cycle?

API Stress Zyme

The biological cycle can be started by adding 2 or 3 very hardy fish to your new aquarium. The hardy fish that you introduce to your tank have small amounts of the bacteria in their digestive tract which will get released into the aquarium.

Both Nitrosomonas and Nitrobacter bacteria live in the substrate of your tank. They depend on oxygen to live. That’s why it’s important to keep your powerheads or air pumps working at all times. They pull air from the water thru the gravel giving the bacteria a continuous supply of oxygen.

Some say not to do it… but you can speed up the biological process by adding gravel from an established tank into the new freshwater tropical aquarium. I’ve done this several times with no problems. The bacteria will spread from the old cultured gravel to the new gravel.

Another proven method of speeding up the biological cycle is by adding Stress Zyme to the aquarium water when you introduce your first fish. Stress Zyme contains over 300 million beneficial bacteria per teaspoon.

How do I know when the Biological Cycle is complete?

Testing, testing, and more testing. You’ll need to buy a water test kit that tests for Ammonia, Nitrite, and Nitrate. The first thing that will happen in a new aquarium is that you’ll see a spike in Ammonia levels a few days after you’ve added your 2 or 3 hardy fish. Keep testing the water every couple of days and eventually, you’ll see the Ammonia level drop and the Nitrite level will spike. This is a good indication that the biological process is beginning to start. Continue testing every couple of days and eventually you’ll see the Nitrite level drop and the Nitrate level will spike.

Nitrate is easily managed by changing 10% to 20% of your aquarium water on a weekly basis.

Where does Ammonia come from?

Ammonia starts the entire process. Ammonia comes from fish respiration, and decomposing organic wastes such as fish feces and left over food particles. It is very harmful to the fish in your aquarium and you must consider keeping ammonia levels to zero. Following are some ways you could achieve it:

  1. Change your water. (For convenient water changing you could opt for investing in FX series filter)
  2. Keep track of water conditions.
  3. Choose the right filter. (Here’s a guide to help you choose the right filter)

When can I add new fish to my Aquarium? – Nitrogen Cycling Timelines

Usually after 6 to 8 weeks its safe to add 2 or 3 more new fish to the tank. Wait a couple of weeks then add another 2 or 3 new fish again. In the meantime keep testing your water. Wait 2 weeks and then add a couple more fish until you reach the population density that your tank can safely handle. To elobrate:

Typical Duration of the Biological Cycling Process

  1. Initial Stage:
    • Introduction of ammonia source and bacterial colonization
    • Typically takes 1 to 2 weeks for the first signs of bacterial activity
  2. Ammonia to Nitrite Conversion:
    • Development of Nitrosomonas bacteria
    • Can take 2 to 4 weeks for ammonia levels to peak and then decline
  3. Nitrite to Nitrate Conversion:
    • Establishment of Nitrobacter bacteria
    • Additional 2 to 4 weeks for nitrite levels to peak and then decrease
    • Nitrate levels gradually rise
  4. Stable Conditions:
    • Once nitrate is consistently present, the cycle is nearing completion
    • The entire process typically lasts 4 to 8 weeks, but variations are common
Follow Bryan:

Bryan, a seasoned aquarium hobbyist, boasts over a decade of dedicated fishkeeping experience. His passion for aquatic life has cultivated a wealth of knowledge, making him a go-to expert in creating thriving and balanced underwater ecosystems. From vibrant fish communities to lush planted tanks, Bryan's journey is a testament to the rewarding art of aquarium care.

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