Understanding the Basics of the Nitrogen Cycle in Aquariums

Nitrogen cycle in the aquarium

The existence of hazardous quantities of nitrogen-containing chemicals in the natural ecological habitats of most common is relatively unusual. However, in an aquarium setting, there is frequently overfeeding and overpopulation in a tiny, enclosed space. These completely sealed habitats encourage nitrogen pollution, which can make your aquarium fish sick or possibly kill them. The nitrogen cycle is made up of these fundamental chemicals and processes.

Nitrogen Cycle

The natural nitrogen cycle is a complete cycle in which nitrogen passes from the atmosphere to plants, animals, microbes, and back to the atmosphere; this system does not require human involvement. However, in an aquarium, the nitrogen cycle is more of a biochemical cascade involving the continuous chemical breakdown of nitrogenous substances like as ammonia, nitrite, and nitrate. The remaining nitrates are subsequently absorbed by or eliminated from the water in various ways.

In natural ecosystems, this cascade shows how natural wastes in water are handled. Even in a closed tank, the enthusiast must build and maintain this cascade. The major biological poisons found in an aquarium are ammonia, nitrite, and nitrate, therefore the nitrogen "cycle" must successfully convert and eliminate all of these waste byproducts.

This cascade develops over time in a live aquarium. It might take up to three months for a fresh aquarium's waste to completely convert to nitrate. The strategy of gradually filling your new aquarium with younger, smaller fish allows the nitrogen-converting bacteria to flourish and keep up with the progressive rise in waste matter.


Bacteria turn fish urea and proteins into ammonia right away (step 1). Ammonia is a colorless, smelly gas that is very poisonous under normal conditions. When ammonia levels get too high, it's usually because the aquarium has too many fish or the fish are being fed more than they require for healthy life. However, in a well-balanced aquarium, bacteria known as "nitrogen-fixing bacteria" will consume (oxidize) the ammonia (step 2) and convert it to nitrite.


Because nitrates are the most common killers of aquarium fish, they are the nitrogen cycle components to avoid. Nitrites are formed in the aquarium when ammonium ions are partially oxidized. Nitrite-loving bacteria subsequently convert the nitrite to nitrate (step 3), making it relatively safe.

The easiest initial step in preventing nitrite build-up is to feed sparingly and keep the tank's population under control. Second, do a partial water change on a regular basis (not more than 20% of the entire volume) with well-aged water rather than tap water.

Third, make sure the aquarium has a reasonable number of total living species. Many newcomers to the aquarium hobby overlook the fact that, while catfish, algae eaters, and snails are "cleaner fish," they all create waste and contribute to total nitrite levels.


The oxidation of nitrogen molecules produces nitrates as a byproduct. Nitrates are primarily formed in aquariums by the decomposition of animal protein and ammonium molecules. Urine, dung, edibles, and the remnants of dead fish, snails, and plant leaves are all examples.

Even huge amounts of nitrates are tolerated well by most freshwater tropical fish and other aquarium dwellers. Feeding carefully and keeping a limited animal population are two preventative strategies to avoid excessive nitrate accumulation.


Aquatic plants may also significantly lower nitrate levels in a properly regulated aquarium since they actively utilize nitrogen. Plants remove and utilise nitrates in a natural ecosystem. The tank owner must remove the tank at this final step of the cascade in an unplanted tank system.