The Nitrogen Cycle in Aquariums

Understanding the Basics of How the Nitrogen Cycle Works

Nitrogen cycle in the aquarium
Thomas R. Reich PhD

In the natural habitats of most common community tropical fish, toxic levels of nitrogen-containing compounds are relatively rare. In an aquarium environment, however, there is often overcrowding, overfeeding, and a ..... closed environment So it is conducive to nitrogen pollution that can sicken or kill your aquarium fish. Here's an overview of the basic compounds that make up the Nitrogen Cycle:

Ammonia Content

Under normal conditions, ammonia is a colorless, pungent gas that is highly poisonous. It easily dissolves in the water where it may in part become altered into ammonium ions and hydroxyl ions. In contrast to ammonia, ammonium ions are only poisonous to fish in high concentrations,

Ammonia is a result of the bacterial decay of urea and proteins, ie, there are too many fish in the aquarium or the fish are being fed more than they need for healthy survival. In an aquarium kept in balance, nitrogen-fixing bacteria eat (oxidize) the ammonia, changing it from nitrite to nitrate and so rendering it mostly harmless.

Nitrite Content

Nitrites are the salts of nitrous acids; nitrites are the killers of aquarium fish and the products that we must guard against in the Nitrogen Cycle. They occur in the aquarium either through the partial oxidation of ammonium through the “reduction” of nitrates. 

The simplest way to prevent nitrite build-up is to feed sparingly, make sure there are not too many animals in the tank. Secondly, regularly carry out a partial water change (not exceeding 20% of the total volume) with well-aged water, not tap water.

Third, make sure there are not too many total living animals in the aquarium. Many who are new to the aquarium hobby forget that even though catfish, algae eaters, and snails are “cleaner fish” each still produces waste and adds to the total nitrate.

Nitrate Content

Nitrates are the end-product of the oxidation of nitrogen compounds. In the aquarium, nitrates are produced mainly through the breakdown of animal protein and ammonium compounds. Examples are urine, excrement, foodstuffs, and the remains of dead fish, snails, and plant leaves.

Most freshwater tropical fish and other aquarium inhabitants are very tolerant of even large quantities of nitrates. However, precautionary measures against too high a build-up of nitrates include feeding sparingly and only having a small animal population. Aquatic plants can greatly reduce the levels of nitrate in a well-adjusted aquarium as well.

Nitrogen Cycle

The Nitrogen Cycle is a biological process that involves the continual circulation of nitrogenous compounds such as ammonia, nitrite, and nitrate to process wastes in the natural water. In a closed aquarium, this cycle must be established in what is commonly called the Nitrogen Cycle.

Ammonia, nitrite, and nitrate are the main biological toxins found in the aquarium, so the nitrogen cycle must work effectively to convert and then remove these byproducts.

This cycle is established over time, it usually takes up to three months before a new aquarium has fully cycled. Stocking your new aquarium slowly over time and with younger, smaller fish is to allow the nitrogen cycle time to develop and keep pace with the gradual increase of waste matter.