I decided to create this thread to post my findings, and to offer a place of discussion for a very important topic. One that is critical and most necessary to any new aquarium, be it saltwater or fresh. I became fascinated with the Nitrogen Cycle while studying it in my Microbiology class, that I am enrolled in this semester. I always understood, or so I thought, the basics of this particular topic. However, through my class sessions, readings of my textbook, research via online creditable sources, and discussions with my professor, I am beginning to understand it more and more. I do want to apologize to anyone on the forum that have been involved with me in any threads where it was being discussed. I have never or will never claim to know it all! I only like to participate, with things that I know in order to further my knowledge. With that being said, I will try to explain my findings with limited science jargon and in order as much as possible so that this thread does not become a boring "research paper." After all, I wish to capture the attention of new hobbyist and experienced ones. Call me biased, but I would not mind also persuading others to join the saltwater world as well! Please, while reading do try to understand what is being presented to you. It is there to help, and you will find that you will only benefit from this post if you take the time to fully understand it. Let's begin!
The Nitrogen Cycle, what is it and why is it important? A very simple question that can be easily answered by most veteran aquarium enthusiasts. From a general standpoint, it is in the most basic sense a culturing and promotion of particular groups of bacteria that target inorganic wastes or organic wastes, to to utilize them for growth. This utilization in turn, benefits the hobbyist by providing a natural way to expel these toxins from their aquatic systems. In an even more generalized sense, without these bacteria our aquatic friends would basically urinate and defecate themselves to death. Call it, an unintentional suicide.
*I would like to make it a point here that one must understand the process of oxidation. Simply put, Oxidation is when one atom or compound steals an electron from another atom or compound*
According to my textbook, "Microbiology: An Evolving Science. 4th Edition", authored by Slonczewski and Foster, Nitrogen Gas (N2) makes up nearly "79% of Earth's atmosphere." Nitrogen or nitrogen gas is considered to be the "blueprint," of life for many cells. However, even though it is plentiful, most organisms find it very difficult to utilize due to the highly stable relationship between the two nitrogen atoms which are held together by a triple bond. In more simple terms, there are two Nitrogen atoms in Nitrogen gas. The nitrogen atom itself, contains 5 individual electrons .These two atoms are held together by sharing 3 of their electrons, and then two electrons are "suspened," on their outer shells. I will try to illustrate it as well: ( :N---N: )
I hope I have not lost you already, it get's easier to understand. I promise!
Let's continue discussing nitrogen. Nitrogen presents itself, in many different forms. It can be organic, which means it is a product that can be found inside living organisms, or in organic decomposition of organic matter. In the main form, we view this as proteins which are made up of amino and nucleic acid. Guess what! These proteins contain nitrogen bases! Nitrogen can also be found in the form of ammonium (NH4+), nitrite (NO-2), nitrate (NO-3), nitrous oxide (N20), nitric oxide (NO) or even inorganic nitrogen gas (N2). Nitrogen balances in a system, by nitrates. As nitrogen is processed to nitrates, these nitrates will leave a system and more nitrogen will enter. We will discuss more of that later! But keep that in mind!
Now we're walking, let's see if we can proceed to a faster pace! This part was a wild goose chase for me, but fortunately for you I can condense it! There's no need to go into families or species while discussing the cycle itself. There are way to many to cover! These bacteria and even some archae, are all related in many ways but utilize different resources and environments to achieve nitrification. They are aerobic (oxygen dependent), anaerobic (non-oxygen dependent), phototropic (utilize sunlight), chemotrophic (utilize specific chemicals), and etc. They are actually present at the surface of the water, in the water's column, and attached to surfaces. They colonize, and create bio-films. They are symbiotic and work alongside fungi, corals, sponges, etc. They also co-exist with other microbes of similar biology! That's way to much to try to figure out and without the help of a professional grade laboratory to examine your aquarium water, we can only at best guess what species may be in your aquarium.
However, what is important is that they all have a similar enzyme complex called nitrogenase
! This particular enzyme is what catalyzes, or initiates, the oxidation of nitrogen gas to ammonia! Congratulations, we can now discuss the first step of the cycle.
The first step in the cycle, is called Nitrogen Fixation
! This happens by a specific group of bacteria or in some cases Archea, and they use oxidiation. Basically, we're "fixing" nitrogen gas (N2) at the surface level and turning it into Ammonia (NH3
). This is all by the transfer of electrons! If you are very interested in that process, I would just google how oxidation occurs. Trying to explain this multiple times through the remainder of the thread will probably cause confusion. However, from my understanding, and to be noted, when nitrogen is "fixed" via the protein breakdown way, ammonium nitrate (NH+4) is produced! It all works out in the end. So no need to worry! To put into a better perspective, if we do a fishless cycle we can achieve success by introducing a fabricated but pure source of ammonia purchased from a local store, into our aquarium. If we still do a fishless cycle, but however we introduce a protein source such as a raw shrimp, we still achieve the same results but this time the microbes just utilize ammonium. It would be a similar process to a fish in cycle, but with much less work and stress, in my opinion. Either way, all these processes help initiate or jump start the cycle for quicker results. We could set up our aquariums and just wait for these microbes to set themselves up, and begin utilizing nitrogen gas which is already present in our homes. But this could be a lengthy process, which actually does happen! My tank for example,was set up and running! Due to my current situation I was never able to introduce fish or a source of ammonia. Over the months, biofilms and algae started to bloom. Now I know why! Nature adapts, and it can be fascinating.
Our second step is to convert ammonia or ammonium to nitrites. Much less toxic than the two, but still pretty rough. These process is nitrification
! We can call these microbes ammonia-oxidizers! Because they are doing the same thing that ammonia did to nitrogen. Except now it is happening to ammonia or ammonium. This happens by intermediate hydroxylamine, a process that requires two different enzymes, ammonia monooxygenase and hydroxylamine oxidoreductase. We'll stop there with that! No need for the added confusion.
Finally, we are closing in on the light at the end of the tunnel. We are going from nitrites to nitrates. Nitrates being the most harmless of the three toxins, but still toxic in high levels! These microbes are considered nitrite-oxidizers! Good news too, I don't have much in the way of explaining any complex processes or enzymes involved here. I could not find any information on that. Maybe someone else can! All we need to know is that this part is conducted by another microbe and they oxidize nitrite into nitrates!
Now, we have reached the end. This part is called dentrification
! Many different organisms or methods take place here. Basically the nitrates build up in the water column until they have reached an equilibrium. Remember that nitrogen takes many forms and we are just changing forms to help these microbes utilize nitrogen in order to grow. We are recycling it! When this equilibrium is reached nitrates leave the water by physical water changes, consumption by plants or algae, aquarium chemical filtration, or by being converted back to nitrogen gas by another microbe where it leaves the water's surface! Thus you have your balanced system.
I do hope this was not to much, and that it is as close at to the truth as possible. I did put in a lot of time and tried to use reliable resources! If I have missed anything, please feel free to add. If you have a question, please ask! Failing to provide this for an aquarium is what causes many to leave the hobby before they start. Overall, it is a fairly simple process accomplished in many different ways. I plan to do research on other topics, and I do not mind posting it here. Let me know what you all think, and good luck with your tanks!