Everyone has heard about ammonia, nitrite, nitrite bacterium, ammonium, etc, but, do we really know how they work? We will try to explain it the easiest way possible, especially for those who are just beginning with the fascinating world of aquariums. The fish in the aquarium excrete in form of ammonia and urea, which are also found in rests of food, rests of dead plants and dead fish.

All of this rests produces ammonia (NH3) in aerobic conditions (with oxygen) and in anaerobic conditions (without oxygen) produces, besides the ammonia, hydrosulfuric acid, methane, phenol, etc, all very dangerous to fish. The zones that do not have any oxygen are mainly in the gravel, so we must keep an eye on this. As far as ammonia (NH3) is concerned, you must also know that a dissociate form exists, that is the ammonium (NH4), which is about 100 times less toxic than the gaseous not dissociate form, NH3. The fact that we have ammonia or ammonium depends on the pH and temperature of the water, the more pH and temperature, the more ammonia we will have, and the less pH and temperature, the more ammonium. With a pH of about 8.2 and a temperature of 25 °c, we have a pretty safe environment for our fish in case of an ascent of ammonia, because with these values, it will be in the form of ammonium. Ammonia causes a swelling in the fish’s gills, whose laminates unite causing asphyxia.

Thanks to the presence of nitrite bacterium the process of transformation of ammonia into ammonium will begin, this is taking care of by the nitrosomona bacteria which consumes ammonia and oxygen and turns them into nitrite (NO2), water and Hydrogen. Nitrite is not has deadly as the ammonia, but it is equally dangerous, because they mix with the hemoglobin of blood, and as this can not carry oxygen, causes asphyxia in fish. Finally, thanks to the nitrobacter bacteria that takes care of the reaction that transform nitrite (NO2) intro nitrate (NO3) consuming oxygen, these no longer represent any danger to sweet water fish, unless they are found in very high concentrations (100 mg/l). These are eliminated because they are consumed by the plants, through changes of water (be careful not to put water that contains more nitrate that the one we are removing) we can also use a filter that removes nitrates from the water turning nitrates into free nitrogen. This process is carried out by some anaerobic bacteria (that does not need oxygen) that use nitrate as their food, collecting the oxygen, they free nitrogen, but this process can not be done inside the aquarium for the obvious reasons, that is why we must use an outside filter, which we do not recommend unless you have a very big aquarium, given that sweet water fish, even when nitrate is toxic, can tolerate high doses of it. If the accumulation if nitrates where very high, from 3000/4000 mg/l, we could have a turning back, with nitrates and nitrites turning intro ammonia, but this can only happen if we really neglect our aquarium.

Maximum levels during nitrification of sweet water:

Ammonia (NH3): 0.01 mg/liter

Ammonium (NH4): 0.1 mg/liter

Nitrite (NO2): 0.2 mg/liter

Nitrate (NO3): 1000 mg/liter (or even higher)
Knowing how this process works, we can tell that when we have nitrites it means that there was ammonia before, and the other way around, if we have ammonia we know we had nitrites before, unless the bacterial colony is already fully settle and the intermediate toxic products do not appear.

An aquarium is fully settled usually after a month or so since we started it, now, an excessive increase in the density of animals, habits of food, excessive siphoned, medical treatments or even an accident (that we drop the whole bottle of food into the aquarium) can require another maturation process of the aquarium. During these processes we must be very careful incorporating new fish.

A very important point is do not clean up on the same day the filters, the gravel, the decoration, etc, do one thing per week, and remember that an excessive cleaning can be fatal to the aquarium.

One thing to keep in mind is that in the water at the most there is a 1 or 2 % of the total bacterial colony of the aquarium, bacteria fixes on filters, gravel, porous decoration and even in plastic plants; which is why if we are going to set a new aquarium is always more important that we put in it all of these old components than part of the water of the old aquarium.

Now that you know a little more you will understand why it is recommended to populate the aquarium slowly, this is simply to give the bacteria time to adjust to the amount of fish, and so it can absorb all of the organic matter that are in the aquarium. Remember to not over populate the aquarium, there is a limit you can not exceed, if you do you may have some casualties within your fish.


One of the secrets of the aquarium is patient – DO NOT RUN –
An aquarium that does not start its cycle properly has very little chances to succeed.
Be careful with the food, food excess KILLS.
It is better to feed the fish several times a day in little amounts than a lot just one time a day.
Populate the aquarium slowly, do not fill it up with fish on the first day, we have already told you, be PATIENT.
When we feed the fish we should take a look at them, lack of appetite is a symptom of something going wrong.
Every month we will change the water, about a quarter or so of the total. Remember that it is not the same to add the amount of water that has evaporate than to make a change of water.
Be careful with the incompatibilities of our fish, when we go shopping for a new specimen, we must indicate the ones we already have. As a rule, the bigger fish will eat the smaller one.
It is good that we provide the fish with a varied food of high quality, including alive and frozen food.
If your aquarium has a plate filter do not even think about making it stop, within a couple of hours you can destroy the entire bacterial colony.
If we see white foam on the top of the water inside the fish globe, we should have the water analyzed, there could be ammonia.
Every time we suspect there is ammonia or nitrites in the water, we should rapidly make a change of water.
If by some reason (illness, aggressiveness, etc) you wish to get rid of a fish, do not floss it down the toilet, or kill it by stepping on it (we know more than one case), just put it in a plastic bag with a little water and try to take it to an aquarist, he will surely be able to do something.

We hope that what we tell you can help you, keep in mind that for every four persons that enter the aquarium world, three give up on this beautiful hobby during the first year. What we want is that you are not one of those three.

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