In a closed system like the aquarium, the cycle takes 36 days and is divided into three stages.
At the first stage, the breakdown of proteins forms Ammonia, which is toxic. Proteins usually come from fish fecal matter and rotting organic matter, such as plants, bacteria, and surplus food.
Then ammonia is transformed into nitrites, which, while toxic to fish, will then become less harmful nitrates. Plants consume these nitrates as fertilizers.
Plants then grow and generate dissolved oxygen in the water, closing the nitrogen cycle. If you do not have plants, nitrates also help the growth of colonies of beneficial bacteria in filters.
If there are surpluses of nitrates, they are removed in water changes.
It should be noted that in the installation of planted aquariums the Nitrogen cycle is not fulfilled as described above. The presence of plants and rapid generation of colonies of bacteria modify the conditions of the aquarium, altering this process.
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