Activated carbon for water purification.
Activated carbon is made from anthracite or coal, wood, silicon compounds (silica gels), and other materials such as bamboo, coconut shells, and fruit tree pits. First, it is heated to a high temperature in the absence of air, then activated at an even higher temperature, up to 1000°C in the presence of steam, air, etc. The result is an extremely porous material. The pores in activated carbon have volume and, accordingly, surface area. The level of activation of carbon is determined by the total surface area of all pores present in one gram of carbon. During the manufacturing process, it can be washed in various substances and acids.
Activated carbon is a special filtration mass which, due to its special properties and specific manufacturing method, has the ability to remove high-molecular organic compounds from water through surface adsorption. In aquarium practice, activated carbon is used both in aquarium filters and for water preparation.
Activated carbon is one of the most common filter media and is used for chemical filtration. The use of carbon makes it very easy to achieve good water clarity in the aquarium; carbon is also used after fish treatment to remove drug residues from the water. Activated carbon exerts its beneficial effect due to the fact that it has a large number of microscopic pores and, thereby, absorbs (absorbs and adsorbs) organic molecules from water. It is especially effective for filtering organics that give water a yellowish color and odor. In addition to toxic compounds, it also absorbs acids (peat), various dyes and medications, and therefore filtration with carbon cannot be combined with the addition of acids or medications.
Synthetic activated carbon is a form of synthetic activated carbon, differing in that (including “Bio Chem Stars” stars from Aquarium Pharmaceuticals) its pores are through-pores. Due to this, a favorable microclimate is formed, creating optimal conditions for the development of bacterial colonies. As a rule, the “stars” are colored dark to prevent the penetration of bright light, which suppresses the development and activity of nitrifying bacteria colonies. The presence of a large number of pores (ranging from 50 to 120 microns in diameter) increases the total surface area by more than 30 times.
A unique macroporous synthetic material that removes soluble and insoluble substances at an adsorption speed and capacity five times higher than other absorbents. It has all the advantages of activated carbon, but without its disadvantages. It absorbs about three times more organics per unit volume, taking up much less space in the filter. It is not intended for mechanical filtration. It floats in water. They can be combined with other filter media.
It is also effective for removing heavy metals from water and chlorine during osmotic filtration. Activated carbon does not remove ammonia/ammonium, nitrates, and phosphates from water – other media are needed for this (for example, zeolite). This filtration method has disadvantages: • Over time, activated carbon becomes exhausted and has to be replaced with new one; • Also, the efficiency of chemical filtration decreases over time due to the clogging of carbon with small debris particles. If the carbon is clogged and blocked with dirt particles, there is no point in it; • Old, untimely replaced activated carbon leads to a decrease in the redox potential.
This is what activated carbon granules look like under a microscope
The effectiveness of activated carbon in an aquarium depends on many factors:
The type of carbon used – try to use good carbon designed for aquariums. Other types of activated carbon can release harmful substances into the water. The best adsorption properties are possessed by so-called molded carbons, i.e., pieces of various sizes pressed from coal dust. Try to avoid using carbon from drinking filters. Carbon that is part of cartridges for drinking pitcher filters may be washed in phosphate-containing acids during manufacture. It has a low pH value (to suppress bacterial growth in it), so it will “acidify” the water and release phosphates that promote algae growth.
The type of substances being removed and the water flow rate – molecules of different sizes are removed with different efficiencies (smaller molecules faster). The water purification speed depends on the concentration of the substance being removed – at high concentrations, removal occurs faster, but less time is needed to remove a smaller amount. The slower the water flows through the carbon, the longer the contact time and the more efficient the removal. On the other hand, in a closed system, water passes through the filter multiple times.
Carbon particle sizes and porosity – efficiency depends on the ratio of pore volume to carbon volume. The more pores, the more effective the carbon.
The time the carbon spends in the filter. As it is used, the carbon’s efficiency decreases because the pores become clogged. On the other hand, bacterial and organic films growing on the carbon also reduce filtration efficiency. Dirt is the worst enemy of activated carbon and its porous surface. Therefore, the carbon filter in the general filter chain must certainly occupy the last place, and all mechanical cleaning processes must be carried out in advance. Try to use a mechanical filter before the carbon to filter out large dirt particles and protect the adsorbent from premature contamination.
Do not leave carbon in the aquarium for a long time, especially when filtering out toxic substances or antibiotics used to treat fish. Although it rarely happens, carbon can begin to release previously absorbed substances back into the water. It should also be borne in mind that in addition to unwanted impurities, carbon also “collects” many useful trace elements, and this can lead to their acute deficiency. Therefore, carbon (as well as other filter media) must be regularly washed and replaced. In general, is it necessary to keep carbon in the aquarium filter constantly? Probably no than yes. In our opinion, only its periodic use makes sense. For example, after a course of treatment with a medication.
How to choose good activated carbon? Carbon regeneration.
Air diffusers, Supply tubes, Splitters, Check valves. 
