The ammonia or nitrogen cycle keeps aquarium fish alive

Ammonia TEST RESULTS: Cycle Fish Tank using Fish Tank Aquarium Nitrifying Bacteria
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Once the nitrogen cycle has stabilized as indicated by the above readings, you can introduce more fish into the tank gradually. Water tests should still be taken weekly, or whenever the water appears murky or when problems are suspected. Increasing the number of fish will alter the chemical readings temporarily. This illustration is based on adding a "few hearty fish" to begin the stabilization process. If you add a larger number of fish in the tank during the initial few weeks, you are endangering your aquatic life and it will take longer to stabilize the nitrogen cycle. It is important to have your aquarium well-oxygenated. Nitrosomonas bacteria need oxygen to develop and grow. Without the oxygen, harmful ammonia and nitrites build up more quickly.
With the ammonia drop method, all aquarium types can be cycled in a very short period of time.
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The nitrification cycle is actually pretty simple. It can seem hard because of a couple terms that are not familiar in our everyday language. But basically this is a simple three-step process. The time it takes to cycle an aquarium can be sped up by 'seeding' the aquarium with commercially prepared bacteria. Then the entire cycle will only take between 1 - 2 weeks. This seed bacteria is available in either a freeze dried or liquid form. You can also add bacteria rich media from an established aquarium, like some of the gravel. The seeding should be done after ammonia is starting to form in the newly setup aquarium. You must wait until there is ammonia or the seeded bacteria will starve. Use ammonia to cycle your marine aquarium without putting delicate and expensive livestock at risk.
Photo provided by FlickrUse ammonia to cycle a new aquarium without putting fish at risk.
Photo provided by FlickrIf you prefer to cycle a saltwater aquarium without using fish you can use fish food or ammonia
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Many aquatic animals secrete nitrogenous waste products in the form of ammonia. Furthermore, uneaten food and other wastes produce ammonia as they decompose. In a healthy aquarium, bacteria then feed upon the ammonia and turn it into nitrite (actually HNO2, nitrous acid). Then a second group of bacteria turns the nitrite to nitrate (actually HNO3, nitric acid). This process is depicted in the cartoon below. Ammonia and nitrite are toxic to aquatic animals, and this is where the main problems with new aquariums occur. The term cycling refers to the establishment of an active "biological filter" (or "biofilter") consisting of beneficial bacteria that break down nitrogenous aquatic animal wastes. In a brand new (un-cycled) aquarium, the levels of ammonia and nitrite will rise, and these toxic compounds can reach lethal levels. Once the bacterial populations become established, they break down these compounds into non-toxic forms, and the tank is then considered to be "cycled". It can take anywhere from several weeks to a couple of months to cycle an aquarium.The majority of established aquariums were cycled with fish or other aquatic organisms. While this is an effective way to cycle a tank, it can be lethal to the animals unless conducted properly. Some hobbyists consider this method cruel, as it exposes the animals to ammonia.Graph(click to enlarge) of ammonia, nitrite and nitrate concentrations versus time in a typical nitrogen cycling pattern of establishment. Initially (1) there is no ammonia in a new system. With time going by, addition of exogenous ammonia, a bit of food, some live rock... ammonia accumulates and populations of chemo-autotrophic bacteria that can utilize it as well. As these first ammonia-utilizing micro-organisms increase in number, their by-product of nitrite (2) begins to accumulate triggering the beginning of a second group of species of nitrifying bacteria (3) that begin to populate the aquarium, converting the nitrite into nitrate aerobically (4). At time/point 5 ammonia starts to drop off in concentration, being readily oxidized by the first group of nitrifiers. Ditto at time/point 6 for the second group of bacteria. At time seven the system has officially "cycled" with ammonia and nitrite now at undetectable levels. In completely cycled, balanced systems the curve of nitrate concentration will flatten as marked (8) with an unbalanced situation (too little denitrification, use of nitrates by other life, transport by water changes, over-feeding/under-filtration...) accounting for an ever-increasing level/concentration of nitrate as indicated by (9)As an alternative, the tank can be cycled without any animals in the aquarium. For this process, you will need test kits for ammonia, pH, nitrite and nitrate, and a source of ammonia. Possible sources for the ammonia are easily decomposed materials such as frozen brine shrimp.