A thorough understanding of how water quality affects animal life is essential if one is to be a successful aquarist. This is sometimes a bit difficult for beginners to accept, but please remember that it is a serious mistake to spend time learning about the habits and dietary needs of aquatic creatures while ignoring the “less glamorous” aspects of the hobby. Once you understand water chemistry basics, your appreciation of how fishes and invertebrates survive in their environments will be heightened.
The Nitrogen Cycle
The nitrogen cycle is a critical factor in the establishment of a crystal clear, well-balanced aquarium. Poor functioning of the nitrogen cycle is undoubtedly the most common reason behind new aquarium failures.
Basically, the nitrogen cycle is a process by which nitrogen is converted to other organic compounds that are then utilized by plants and animals as food. Nitrogen enters the aquarium via dead animals and plants, uneaten food, and the waste products of fish and invertebrates. The most toxic nitrogenous compound that is added to aquariums in this manner is ammonia. Ammonia occurs in two forms, ionized and un-ionized, with the un-ionized type being extremely toxic to aquatic organisms. The proportion of the total ammonia that is un-ionized rises as the water’s temperature and alkalinity increases.
Bacteria and the Nitrogen Cycle
Two types of bacteria control the functioning of the nitrogen cycle. These bacteria are aerobic, which means that they require oxygen in order to survive. Bacteria populations develop and thrive on substrates that are exposed to oxygenated water, such as gravel and the filter pads and carbon within filters.
The process by which aerobic bacteria convert ammonia to less harmful compounds occurs in two phases. Nitrosomas bacteria convert ammonia to compounds known as nitrites. Nitrites, while dangerous to aquatic organisms, are less toxic than is ammonia. In the second stage of the process, bacteria of the genus Nitrobacter utilize these nitrites as food, and in doing so convert the nitrites to nitrates. Nitrates are the end product of the nitrogen cycle, and are the least toxic of the compounds involved.
Nitrogenous bacteria (the name given to the various species of bacteria that feed upon ammonia-based compounds) exist in huge populations in natural water bodies and in healthy aquariums. Until such are established in your aquarium, its levels of nitrogen-based compounds will be toxic to nearly all fishes and invertebrates.
The time it takes for healthy populations of nitrogenous bacteria to become established in an aquarium is often referred to as the “conditioning period”. Its actual timetable varies greatly depending upon the unique characteristics of each aquarium and of the animals therein, but usually falls in the range of 1-6 weeks.
Please bear in mind that water clarity is not an indicator of the functioning of the nitrogen cycle. The only sure way to monitor the cycle is via frequent testing of the water to determine the levels of ammonia, nitrates, and nitrites (please see below).
Altering the Nitrogen Cycle
Your aquarium’s conditioning period may be shortened by the addition live aerobic bacteria. I have had good experience with Biozyme Freshwater and Biozyme Saltwater, and strongly urge you to use either with all new aquariums. Products such as Coral Vital LSB Pro, which accelerates the growth and reproduction of bacteria in marine aquariums, should also be considered.
You can also help the process along by adding filter material from a well- conditioned, parasite-free tank into the filter of your new aquarium. Natural materials such as “live rock” and “live sand” also host beneficial bacteria and offer another option.
In the past, it was standard practice to use hardy fish, such as domino damselfish in marine aquariums or guppies in freshwater aquariums, to hasten the conditioning period (their waste products started the process and provided food for bacteria). However, additives such as those mentioned above are more effective and infinitely kinder, as many of the fish subjected to this process did not survive.
When cleaning your filters, always retain a bit of old filter medium (carbon, floss) and add this to the clean filtering material. In this way, you will introduce aerobic bacteria into the newly-cleaned filter. These will reproduce rapidly and greatly increase filtration effectiveness.
Please be aware that the addition of packaged bacteria does not eliminate the need for a proper conditioning period. Water quality must still be monitored carefully, and animals should be introduced to the aquarium in small numbers.
Measuring the Levels of Nitrogenous Compounds
The frequent use of test kits is essential during the aquarium’s conditioning period, and on a regular basis thereafter.
Ammonia should be tested daily until you notice a sudden decrease in its level. This decrease signals the presence of Nitrosomas bacteria. Nitrate levels will then follow the same pattern, as the Nitrobacter bacteria become established.
The conditioning period may be considered at an end once the nitrate levels drop substantially. You may now begin to introduce fish and invertebrates into their new home. Be sure to add animals in small quantities, so as not to overwhelm the nitrifying potential of the bacteria present, and observe them carefully for signs of stress.
The pH level should be checked often as well, since the water may become acidic during the conditioning period.
I am very interested to hear about your successes and challenges in establishing new aquariums, and will be sure to pass along your information to my readers in future articles. Thanks, until next time, Frank.
An interesting technical article on the role of nitrogenous bacteria in natural marine habitats is posted at: