Nitrogen Cycle for Axolotl Tank

The Nitrogen Cycle is the bio-geo-chemical cycle that converts nitrogen into multiple chemical forms through both biological and mechanical processes. 

The process involves ammonification, nitrification, denitrification, and fixation; though nitrogen forms 78% of the earth’s atmosphere, it has very little biological process use. 

Clean water is fundamental for any aqua life to thrive; the Filtration in an aquarium can be mechanical, chemical, and biological. The Nitrogen Cycle deals with or processes the chemical and the biological part of aquarium water purification. In other words, the nitrogen cycle is the process that takes place in converting fish wastes from toxic to less toxic or non-toxic.

This biochemical process involves continual biodegradation from Ammonia to Nitrite to Nitrate. In this, nitrate is the least toxic nitrogenous compound; the permissible limit for nitrates in water is between 20 to 50 ppm. 

The aquarium plants control the nitrates level in the water by absorbing, and the excess nitrates are taken care of by the periodic water changes.

Axolotl expels ammonia through their urine and feces produce ammonia while decomposing; furthermore, the leftovers and decomposing plants produce Ammonia—the nitrifying bacterium, aerobic bacteria that convert inorganic compounds into their energy source. The Nitrification process requires two different microorganisms; bacteria or enzymes that convert ammonia into nitrites, Nitrosomonas, Nitrosospira, Nitrosococcus and Nitrosolobus, and the bacteria that convert nitrites into nitrates are Nitrobacter, Nitrospina, Nitrococcus.

Ammonia is noxious to fish and invertebrates or any aqua life; it can damage the gills and cause respiratory problems; at times, it can kill your axolotl.

Without a Proper Nitrogen Cycle, an aquarium would be a pool of toxic concoctions that cannot support any aqautic life  as an aquarium is a closed-loop ecosystem.

Hence, understanding the Nitrogen Cycle in an aquarium is the prerequisite for you to benefit from the fish-keeping hobby.


Ammonia in your aquarium

The microorganisms that deal with Ammonia in the natural environment do not exist in the new tank as there is no food for them to feed on. A fishless cycle instigates developing the enzymes/bacteria; a filtration system houses these good bacterias.
A filtration system is not just to filter out solids and suspended particles from your aquarium water; it has several utilities, one of which is housing good bacterias/enzymes to digest Ammonia. All the filter media, sponge, ceramic, candle provides a home for these good bacterias; these bacterias thrive on Ammonia; develop and multiply in response to Ammonia’s presence.
Even a trace of Ammonia could burn your axolotl, which is commonly known as Ammonia Spike. Many axolotl owners wonder why their axolotls don't have any gills, gill fluff, or appetite. Ammonia spike is the common cause for these symptoms. 


Nitrite is the byproduct of digesting Ammonia; it is fatal to your axolotl. Nitrites fuse with blood cells that oxygen molecules are supposed to attach; hence, they prevent absorption of oxygen into the blood adequately and suffocate the fish. All the organs and tissues slow down or arrest functioning as they cannot receive adequate oxygen. Thus, causing organ failure. 
However, nitrites’ presence promotes the colony of bacterias,  Nitrospira; your aquarium filter houses them along with Nitrosomonas.
Nitrospira converts nitrites into nitrate, a less harmful compound to the fish and invertebrates unless allowed to build beyond 50 ppm.


Nitrate is the end result of nitrogenous compounds. In an aquarium, nitrates are the byproduct of the breakdown of axolotl waste,  leftover food, and plant matters.
Axolotls are tolerant to nitrates to some extent; you would want to keep it below 40ppm in your aquarium.

Aquarium Plants

The aquarium plants absorb nitrates ions and leftover ammonium ions to make their amino acids for synthesizing protein; thus, aquatic plants majorly keep the nitrates level in the aquarium water under control. An aquarium tank without live plants will have to do partial water change more frequently.
In summary, the Nitrogen Cycle in an aquarium breaks down organic waste, such as axolotl excretion,  leftover food, and plant matter into Ammonia into Nitrite into Nitrates; absorption of nitrates by the plants or elimination through periodic water change.

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