How does ammonia get introduced to an aquarium?

Chart 1. Typical patterns of ammonia, nitrite and nitrate in a new aquarium.
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First, many ammonia removers are acids, so repeatedly adding them to the aquarium water will cause the pH to drop. This in turn means that the ammonia is in the ionized form (NH4+), which is the form the nitrifying bacteria CANNOT use. So the amount of ammonia converted to nitrite is less per day than if the pH were higher.
I am with Byron,,I would not expect to see ammonia in cycled,moderately planted aquarium.
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The next problem that will occur is one that I believe gets little attention in the hobby but is probably responsible for more fish deaths than ammonia toxicity. This problem is high nitrite concentrations. Once the bacteria that convert ammonia to nitrite (called ammonia-oxidizers) start working, the nitrite concentration in the water will start to increase rapidly. Unfortunately, the bacteria that convert nitrite to nitrate (the nitrite-oxidizers) are even slower growing than the ammonia-oxidizers. In our research, we saw that the nitrite concentration in the same newly set-up aquaria, as described above, reach concentrations of nearly 10 mg/L. Furthermore, the nitrite levels stayed high for several weeks. Usually the nitrite concentration does not drop before 0.1 mg/L until 25 to 30 days after the aquarium is first set up. Ammonia in aquaria has 2 forms.  and .
Photo provided by FlickrA very informative and enlightening article for people who are in the dark about how to remove ammonia from aquariums
Photo provided by Flickr1. Nitrosomonas bacteria convert ammonia to nitrite, nitrospira bacteria convert nitrite to nitrate, water changes dilute nitrate in the aquarium.
Photo provided by Flickr
Like all living creatures, fish give off waste products (pee andpoo). These nitrogenous waste products break down into ammonia (NH3),which is highly toxic to most fishes. In nature, the volume of waterper fish is extremely high, and waste products become diluted to lowconcentrations. In aquariums, however, it can take as little as a fewhours for ammonia concentrations to reach toxic levels.The simple answer is yes, an aquarium must be cycled properly before you can safely add your fish. It doesn't matter whether the tank is 15 gallons or 500 gallons, it's still got to be cycled. If you were to simply fill your tank with water and then add all your fish at once then there would be such a massive buildup of ammonia, the chances are your fish would be dead within a few days.I would encourage all fish keepers to gain an understanding of the nitrogen cycle as this will help you understand exactly what is going on inside your tank and how you can deal with water quality problems should they arise.The simple answer is yes, an aquarium must be cycled properly before you can safely add your fish. It doesn't matter whether the tank is 15 gallons or 500 gallons, it's still got to be cycled. If you were to simply fill your tank with water and then add all your fish at once then there would be such a massive buildup of ammonia, the chances are your fish would be dead within a few days.Traditionally, there are two ways to cycle a fish tank. Both methods will involve introducing ammonia into the tank which will be the food the bacteria need to survive. The most common method of cycling an aquarium is to use small community fish that produce the ammonia themselves. A kinder, more acceptable way to cycle a fish tank is to use a method called the "fishless" cycle. This also involves adding ammonia to the aquarium, but as a name suggests you do not use live fish. In this article, we are going to use fish as it's probably easier for a beginner to undertake, and we wouldn't be happy with youngsters handling pure ammonia as it can be dangerous. If you would prefer not to use live fish then read this article on how to carry out a fishless cycle.We would recommend that you use small community fish like the Barb. The Tiger and Cherry Barb are absolutely ideal as they are quite a hardy species of freshwater fish and unlike some more sensitive species, won't turn belly up as soon as they are exposed to ammonia. If you are cycling a very small tank less than 20 gallons then you are probably better off using much smaller fish like guppies or neon tetra. Your fish store should be able to give you advice based on what fish they sell.It's important not to add too many fish as this will create a large ammonia spike very quickly which will probably just kill the fish within a few days. For a 55 gallon tank, 10 barbs would be appropriate. For a 75 gallon tank, you could go up to 15, for 100 gallons plus, you're looking around 20 upwards.It's become quite popular to kick start the cycling process by seeding your new aquarium with biological media that already contains live nitrifying bacteria.Some call it the biological cycle, the nitrification process, new tank syndrome or even the start-up cycle. They all are referring to the same cycle - The Nitrogen Cycle. The aquarium nitrogen cycle is a very important process for the establishment of beneficial bacteria in the aquarium and in the filter media that will help in the conversion of ammonia to nitrite and then the conversion of nitrite to nitrates. Check out the aquarium water chemistry page (on the left) for more information on these terms.