Introduction to water quality

Discus are without a doubt one of the more popular of the large cichlids to be kept in home aquariums today, and certainly one of the most demanding. The large size of the Discus places extraordinary demands on the water quality of your aquarium, food is rapidly recycled and returned to your aquarium in the form of urine and feces, uneaten food decays rapidly and can foul the water. These things substantially increase the biological load that a tank must bear, far more than the same tank being inhabited by smaller fishes. While you do not need a degree in chemistry to control your tank as some magazine articles would lead you to believe, you must have at least a fundamental idea of the bio-chemical interactions taking place in your aquarium if you are to sucessfully keep and breed Discus.

The Nitrogen cycle in Nature and Aquaria

There are many common aquaria terms you are likely to hear, things like Nitrite, Nitrate, Ammonia, Nitrogen Cycle, System Collapse and many others. Often the beginning hobbyist does not truly understand what is being talked about and often just nods and tries to follow along. An understanding of each of these items, at least in general principle anyway, and how they relate to your aquarium is of utmost importance if you plan to have a sucessful aquarium. All to often I see hobbyists on the internet say "all my fish died, why?" with no clue as to what has happened. It is rare that the experienced hobbyist suffers this fate, at least not without knowing the cause. At this point I think it is necessary to point out that a true biological cycle only occurs in nature , we can only mimic the biological cycle, and prod our tanks along with frequent water changes and maintenance. Of course in the aquarium we are strictly referring only to the nitrogen cycle which is just a small part of the bigger picture, and not the entire spectrum of biological circumstance that makes lakes, rivers and oceans self sustaining. A true biological system has literally millions of components to take into account as part of the whole. Several years ago when I was on a marine field trip in the south Pacific, we went to an underwater area that ws nothing but flat sand, at a depth of about 20 feet. At first glance one would say nothing was there, but on closer observation nothing could have been farther from the truth. We placed a frame (made of wire) 1 foot square, on the sand and then began to count, catalog and observe all the organisms that were visible there. I personally counted over 100 distinct and different creatures in a single square foot of sand!! And this is just those that could be seen with the naked eye and a magnifying lens. Imagine the thousands of microscopic organisms that occupy that square foot. Each and every one of them contribute to the biological cycle. All life feeds, emits waste, removes something from it's surroundings, performs a function of some kind and then dies. We absorb oxygen and expend carbon dioxide, plants provide oxygen and absorb carbon dioxide. In a large way we are symbiotic with plants, and a lot of other things.

Try to imagine then the complexity of nature, truly stunning isn't it? Perhaps now you can understand then that we can only try to emulate a small portion of this, the nitrogen cycle. Nitrogen makes up 78% of our atmosphere,and yet most living things cannot use the elemental atmospheric nitrogen to make amino acids or other nitrogen containing compounds, and thus derive nitrogen from soil minerals. there are three basic steps to the nitrogen cycle, ammonification , nitrification and assimilation . The nitrogen cycle is the single most important reaction to take place in the aquarium, and you should understand it. In an open biological system, everything is balanced in perfect equilibrium. Food stuffs are eaten and digested, execretion and urine as well as dead fishes and organisms, plants etc. are constantly in a state of reduction by progressively smaller lifeforms, be they other fish, scavengers, insects, multi-cellular organisms and finally by microscopic organisms. Along the way each consumes or absorbs only a portion of the whole, just those items that the organism can metabolize for it's own survival, each according to it's evolution. Nothing in nature ever goes to waste. Those familiar with biology have already realized we are talking about decomposition here. It is natures way of cleaning house. From a technical point of view, decomposition can be defined as the chemical change where a substance is broken down inot two or more substances which differ both from each other and the parent substance in it's chemical identity. Complete decomposition occurs when a condition exists that a substance is no longer cable of being broken down by component, such as ammonia, ammonium and carbon dioxide. thus, all ocuring carbohydrates, fats and proteins are completely utilized. Of the three components, This process is ammonification. Ammonium, which is non toxic to your fish, occurs when molecules of ammonia combine with water molecules (Acids being the catalyst). Ammonia on the other hand is very toxic to your fish, and probably the worst nightmare of beggining hobbyists. Discus and most tropical fishes are extremely intolerant of even small amounts of ammonia in the water. Minute quantities of ammonia will be absorbed by plant life in your aquarium (providing you have live plants) and the majority is oxidized first to nitrite and then nitrate by bacteria that I will discuss shortly. This oxidizing process is the second stage, or nitrification. And finally, when the nitrogen is reabosrbed by plant life, algae etc. this is assimilation and the whole process begins again, or more appropriately it continues in a never ending cycle.

The role of Bacteria in the Nitrogen cycle

The nitrogen cycle would not be possible without the presence of Chemosynthetic Bacteria . This class of bacteria derive their energy from the oxidation of inorganic compounds. Certain genera of chemosynthetics are essential components of the nitrogen cycle, by which nitrogen componds are recycled by nature or enclosed ecosystems. One group oxidizes the ammonia or ammonium derived from wastes/excrement/decomposition into nitrites. This group encompasses the bacteria Nitrosomonas, Nitrosospira, Nitrosolobus and Nitrosococcus. The second group of bacteria oxidizes the nitrites and produces nitrates as it's by product, and is composed of bacteria of the genera Nitrobacter, Nitrococcus and Nitrospina. Nitrate is the form in which nitrogen moves from soil and into the roots of plants. Nitrate will not only be taken in by your live plants, but will also encourage the growth of unicellular algae. In nature, the algae would in turn be the nutritional source for plankton which in turn would be the nutritional source for the fish and so on, making a closed cycle that is self perpetuating.

The Nitrogen cycle in the home aquarium

Obviously an aquarium is far too small to perpetuate a nitrogen cycle as I have explained above, the ratio of body mass to volume of water, plants and other organisms is far to great to go any length of time without assistance. So to have a true biological cycle, a totally self perpetuating food chain would have to occur that would feed all organisms and fish, remove all wastes and never require maintenance. Although idyllic sounding, this kind of system does not occur, and cannot occur in a closed system like an aquarium. Even in the largest of public aquariums such as SeaWorld, with thousands upon thousands of gallons of water, a true biological cycle does not occur, therefore we are required on a regular basis to help nature along. I have read articles in magazines about a "Dutch" system that attempts to build this optimal relationship, but I understand that the system is quite labor intensive and expensive to be of any real use to the average hobbyist.

In our home system, we must deal with the reality of helping along the nitrogen cycle. The first step of this process MUST be the elimination or reduction of harmful biodegradable components in the tank/water, and is the first step of ammonification. the obvious answer being that we regularly remove dead animals, un-eaten foods and any decaying material (plants, feces etc.) that may be in the tank. While this is normal in nature, in a small enclosed environment this can lead to disaster. Decaying components pollute the aquarium water with toxic substances that remain in the water with no natural means of reduction, which dramatically increases the possibility of infection and disease. These waste products and dead animals, if left in your tank can harbor faculative pathogens, such as bacteria of the genera Aeromonas and Pseudomonas. These bacteria are very mobile and can rapidly infest a tank, and worse, they can enter your fish's body through the skin, gills or digestive tract and remain undetected. This is refered to by noted Discus authority Dieter Untergasser as "infection pressure" . The more decaying organic material present in the aquarium, whether caused by overcrowding, or poor maintenance, causes a symetrical increase in Untergassers' "infection pressure". The decomposition process never halts, it is constantly contaminating your aquariums water and filter with it's by products. Further, the decomposition process removes oxygen from the water, and can cause your nitrate producing bacteria to die off, then causing the nitrite level of your aquarium to go up. The potential side effect of which, is walking into a room and finding that you are the owner of a tank of dead Discus.

While it then becomes obvious that we must perform regular maintenance on our tanks, siphoning off the feces, debris and organic materials alone is not enough to properly maintain our system. We must also make frequent water changes as well. Depending on the size and number of fish you have in your tank, water changes could be as frequent as every day.

While organic debris is easy to spot, there are other polutants in our aquariums that cannot be as easily spotted, and is just as potentially deadly. We must consider the effects of proteins on the water, Our major staple diet for Discus is beefheart which is full of protein. Proteins are broken down by the fish and are returned to the aquarium in the form of urine, while proteins from left over foods are leaked into the aquarium water directly. Both forms are converted into ammonium, or ammonium by way of amino acids. As stated earlier, plants will absorb some of this access ammonium, but the rest will remain in the tank and build up. Remember we stated before that ammonium is non toxic in acidic water, but ph and temperature can convert that ammonium into toxic ammonia.

Although most of this may sound complicated, it really isn't. Nitrate and nitrite producing bacteria are inter-dependant on each other to survive. In a well "balanced" aquarium that has proper maintenance, oxygen rich water and an established culture in the filtration system, nitrites, nitrates and ammonia occur in quantities that are almost too small for the average test kit to even register. While this definitely not all there is to know about nitrification or the nitrogen cycle itself, it represents a fundamental understand of how water works. More on this subject will be covered later in the section on filtration.