Why do we need to use carbon in a reef aquarium?
There are organic pollutants that can only be removed from reef aquarium water by active carbon.The reef aquarium is a closed artificial ecosystem where living creatures continually produce organic waste consisting of proteins, fats, carbohydrates, organic acids and phenols.If allowed to decompose the organics will fuel the activity of many unwanted microorganisms in the aquarium, increasing the total oxygen demand (BOD, COD) which will cause a reduction in Redox potential, as well as causing excessive production of CO2 by bacterial respiration, which will reduce pH. Furthermore, there will be an increase in nitrogenous and phosphorus compounds, encouraging growth of nuisance bacteria and eventually of nuisance algae. The accumulating organics also has a significant effect on light penetration, especially in the blue and near UV spectrum that stimulates coral growth.
How does activated carbon filter water?
Scientifically speaking, carbon removes the organics from water by a physical process called adsorption. Within a reef aquarium, the submicroscopic pores of activated carbon is the final stage of the mechanical filtration process, adsorbing the organic molecules that are too small to be removed by even the finest mechanical filters or physically removed from the water by protein skimming. Adsorption can be thought of as the adhesion of a molecule to surface by attractive forces. This occurs within the submicroscopic pores of the carbon because the attractive forces between the organic molecules and the internal surfaces of the carbon are far greater than the attractive forces that keep them dissolved in solution. This will continue until all of the surface area inside the carbon is used up and it becomes saturated with organics.
What is activated carbon?
Activated carbon is an extremely porous material with a sponge like structure but with a very large internal surface area relative to its physical size. It is produced from many organic materials that have a high carbon content such as coconuts shells, nutshells, lignite, bituminous coal or anthracite. The carbon-based material is “activated” through physical modification and thermal decomposition in a furnace, under a controlled atmosphere and temperature. The activation process significantly increases the surface area per unit volume of a fine network of submicroscopic pores which is what gives activated carbon its ability to act as a filter material. The specific source of the carbon and the specific activation process determines the physical characteristics of the finished product. There are many different grades of activated carbon and therefore they must be selected specifically for each and every application.
Some manufacturers quote a Molasses Number, however the molecules in the molasses size range are typically removed by protein skimming and therefore this number is irrelevant when evaluating the suitability of activate carbon for reef aquariums.In the past, carbons have been known to leach phosphate into the water, which is undesirable for a reef aquarium and therefore the lowest levels of Leachable Phosphate are considered better. In reality, as long as the leachable phosphate is below a basic threshold level, any differences below that level is not measurable in reef aquariums and is therefore irrelevant.The cleanliness or dustiness of the product is also a consideration and is measured as the Ash Level. The lower the better as higher levels indicate a larger quantity of particles will be released to the water and a lower actual mass of carbon left to do the filtration. Ash levels are often quoted by manufacturers however it is easiest visualized by viewing the turbidity on adding the carbon to water.In addition to these important indicators, the overall efficiency of the activated carbon will be effected by its physical parameters such as Product Density, TSA, Pore Volume and Mesh Size.Activated carbon produced from lignite and anthracite are not recommended for reef aquariums due to an excessive amount of fine powder released to the water (which may lead to lateral line necrosis “HLLE disease” in some fish). Coconut shell or bituminous coal are the preferred sources.
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