Filtration of water in an aquarium is the main and most affordable way to remove excess mineral and organic matter from it and maintain acceptable conditions in an aquarium for its inhabitants. The process of filtering water can be divided into three components:
1. mechanical filtration, which results in the removal of solid particles (suspension) floating in the water;
2. biological filtration, by means of which the products of metabolism dissolved in it, resulting from the vital activity of the inhabitants of the aquarium, are removed from the water;
3. chemical filtration, with the help of this type of filtration harmful inorganic and organic impurities are removed from the aquarium water, as well as, if necessary, the water parameters are changed by introducing necessary preparations into it;
Water purification in the aquarium is done in steps.
Mechanical and biological cleaning
At the first stage, coarse water purification is carried out using filtering materials to prevent suspended particles.
This is a purely mechanical function that does not carry a biological load.
The filtering filler used at this stage should periodically (at least once a week) be washed in clean running water.
As a filtering filler, various synthetic sponges are usually used, as well as special silicone foam rubber and synthetic winterizer.
At the second stage, biological water purification occurs, which is a multistage process as a result of which highly toxic substances (ammonia, ammonium, nitrite) are converted to low-toxic nitrate.
To do this, use a filler with a finely porous structure with the maximum possible surface area for the settlement of beneficial bacteria responsible for biological treatment.
Moreover, the larger the surface area of the material used, the more efficiently the filter will work.
The first and second stages of filtration are closely related.
Firstly, mechanical and biological filtration can be performed by the same filter.
Secondly, the task of cleaning the aquarium from organic pollution is solved simultaneously: biologically, using nitrification and mechanically, by direct removal of dirt from the aquarium.
Thus, effective mechanical filtration dramatically reduces the load on the biofilter, and vice versa.
By chemical filtration, in aquarium practice, sorption is primarily understood. Depending on the type of sorption, various adsorbents are used – bodies capable of absorbing a substance with their (usually highly porous) surface, and chemical absorbers that bind a certain substance, reacting with it in a chemical reaction.
A separate group is represented by ion-exchange sorbents, passing through which the solution gives them ions of one type and takes an equivalent amount of ions of another type.
The most common chemical filtration using activated carbon as the adsorbent. As chemical fillers, some minerals are included in the group of zeolites, synthetic ion exchange resins and peat.
Ion exchange resins and zeolites absorb nitrates, ammonia, phosphates and some other substances, and harmless ions of chlorine, sodium, sulphates instead of them emit.
Peat contains a rich set of amino acids and tannins. Therefore, its use as a filler slightly reduces the pH value, with the simultaneous enrichment of water with various biologically active substances, so necessary for the inhabitants of "black waters".
Sterilization of water can also be attributed to chemical filtration. The main ways in which the aquarium practice are ultraviolet radiation and ozonation.
To effectively influence the conditions of the inhabitants of the aquarium, it is necessary to have an idea of the processes occurring in the aquarium and the filter.
The main water pollution occurs as a result of feeding the inhabitants of the aquarium. And it does not matter whether the food is completely eaten or its remains have fallen to the bottom.
Non-eaten food and metabolic products secreted by fish are the main suppliers of organic compounds participating in the cycle of biological transformations using various microorganisms (nitrogen cycle).
The first stage of this cycle, called mineralization, is the utilization of complex nitrogen-containing organic compounds to simple inorganic. The result of the decomposition of animal waste products is NH3 ammonia, which is dangerous for living organisms at a concentration of 0.01 mg / l.
Ammonia interacting with hydrogen ions H +, present in water, or with water molecules, forms ammonium ions NH4 +, a less dangerous but also toxic substance.
The ratio of ammonia and ammonium depends on a number of factors. One of which is the active reaction of water (pH). At pH values below 7.0 units, the content of ammonia in water is insignificant. So, at pH = 7.0, the proportion of ammonium is 99.5%, and ammonia is 0.5%.
At pH values of more than 7.0 units, the proportions are already somewhat different. At pH = 7.5, the ammonium content is 96%, and ammonia is 4%, and at a pH value of 8.0, the proportion of ammonium is 92%, and ammonia is 8%.
The temperature of the water can also affect the ratio of ammonia and ammonium, with the same pH value.
At higher temperatures, the ammonia content in the water will be higher. And since most of the inhabitants of the aquarium come from warm tropical waters and, accordingly, the water temperature for their maintenance is in the range of 24 to 30 ° C, ammonia can become a tangible problem.
The second stage of the nitrogen cycle is called nitrification, it is a process of biological oxidation of ammonia and ammonium ions, first to NO2 nitrites, and then to NO3 nitrates.
These processes take place in an aerobic environment (i.e., rich in oxygen) under the action of nitrifying bacteria present in the aquarium. The main role of the nitrification process is to convert highly toxic nitrogen compounds (ammonia, nitrite) into low-toxic compounds (nitrates).
Nitrates are also harmful to aquatic organisms, but their action is much weaker than that of ammonia and nitrite.
Nitrates are the final product of the nitrification process, since they are no longer split, but only accumulate in water, negatively affecting fish.
To reduce the concentration of nitrates in the aquarium can be by replacing part of the old water to fresh.
An important role in the absorption of nitrates is aquatic vegetation.
Unlike nitrates, nitrites are poisonous even in small doses. Their maximum concentration should not exceed 0.1 mg / l. Since even a short stay in such water can cause damage to some internal organs of the fish.
How is the nitrification process?
The main role in the nitrification process is played by aerobic bacteria present in both freshwater and saltwater aquariums. These are usually representatives of the genera Nitrosomonas and Nitrobacter.
The first group of bacteria oxidizes ammonium to nitrite, and the second converts nitrite to nitrate. Bacteria live thanks to the energy derived from these processes.
In both cases, a large amount of oxygen is required, especially in the oxidation of ammonium. If nitrifying bacteria get less oxygen than they need, then the nitrification process is less productive. So according to the data provided by M.Sander (“Aquarium technical equipment”, 2002), when the oxygen content in water is 2 mg / l, only 40% of the maximum possible nitrification occurs. While at 4 mg / l, 86% is already reached.
Both aerobic and anaerobic bacteria are always present in the filter media. With a sufficient amount of oxygen, the activity of aerobic bacteria increases, with simultaneous deactivation of anaerobic bacteria.
Conversely, as the oxygen content decreases, the number of anaerobic bacteria increases.
Water is the main supplier of oxygen, it always flows along the path of least resistance. In the silted filter, with obvious impassable zones, undesirable anaerobic processes begin to develop.
Therefore, it is important to timely and properly clean the filter.
In order for the nitrification process to proceed with maximum efficiency, it is necessary to create an oxygen regime in the aquarium at which the concentration of dissolved oxygen would be at least 6 mg / l.
The nitrification process can be affected by a number of parameters:
The most favorable for the development of nitrifying bacteria is in the range from 20 to 30 ° C, with warmer water being preferable.
It should be remembered that in warm water, oxygen dissolves worse than in cold. So, at a temperature of 30 ° C, the maximum amount of oxygen dissolved in water is about 7.4 mg / l.
With the greatest intensity nitrification proceeds in an environment with a pH from 7.5 to 8.5.
According to S.Spott ("Content of fish in closed systems", 1983), the optimum pH value for the oxidation of ammonium is 7.8, and for the oxidation of nitrite – 7.1. In water having a pH below 7.5, the intensity of ammonium oxidation decreases: for example, at pH = 6.6 nitrification is only 85% of the optimum.
Due to the fact that the treatment of fish is often carried out in the general aquarium. Drugs introduced into aquarium water affect not only pathogens, but also beneficial microorganisms.
In some cases, this leads to a complete blockage of the nitrification process.
Different data are given in the publications, but in fact everyone agrees that nitrification is stopped when using drugs such as methylene blue, erythromycin, potassium permanganate, sulfanilamide, etc.
Bacteria involved in the nitrification process are fairly resistant to fluctuations in water salinity. However, nitrification proceeds more actively in fresh water.
Organic "load" on water
Each biofilter, depending on design features, quality of filtering fillers,
in relation to various external conditions (water temperature, pH, etc.) will have a certain cleaning potential.
If the organic load on the filter exceeds its capacity, then there is a real threat of a surge in the concentration of ammonium and nitrite. On the other hand, with a low organic content, beneficial bacteria can be left without food. As a result, their population degrades and its restoration (for example, with an increase in the number of fish in the aquarium) will take some time, during which the values of ammonium and nitrite dissolved in water may also increase.
In a long-running balanced aquarium, the activity of the bacteria that inhabit the filter is balanced with the amount of organic matter entering the water. In such a system, the processes of mineralization and nitrification usually take place simultaneously, and the ammonium content in water is no higher than 0.01 mg / l, and as for nitrites, only traces of them that are the result of uncontrolled denitrification are caught.
But in a newly equipped aquarium (or in an aquarium with a thoroughly washed filter). Ammonium and nitrite can be a very real and big problem.
Therefore, the launch of the aquarium always requires special attention from the aquarist.
In the new aquarium, always have consistently peak values - first ammonium, and then nitrite. And only after the appearance of sufficiently high nitrate values, it can be concluded that nitrification works effectively.