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Author:  Richard M. Greenfield. Bob Straughan.
Title: Activated Carbon
Summary:  Both authors are enthusiastic about the benefits of activated carbon, but emphasise that quality and correct usage is important.

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Date first published: 2000
Publication: Contributed by Calypso Fish & Aquaria Club, London England
Reprinted from Aquarticles:
July 2003: translated into Hebrew language, with added photographs, by Kfir Alfandary of the Israeli Fish Forum in Tel Aviv, at:
Sept 2003: Posted by the Goldfish Paradise Society on
Sept. 2005: Posted by Mike Talbot, of England, as part of the database of his msn group: africanriftlakecichlids.
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Gerald Jennings,
c/o Calypso Fish and Aquaria Club
2 Gatcombe Road,
London  N. 194PT
#205 - 5525 West Boulevard
Vancouver, British Columbia
V6M 3W6

Activated carbon article #1:

Activated Carbons / Charcoals - The Rundown

by Richard M. Greenfield
First published in the (now closed) British Marine Aquarists Association Journal

Using the word carbon to a group of aquarists is almost sure to start a lively debate between those who use carbon regularly with excellent results and the others who point out that it removes trace elements, inhibits the growth of algae and isn't necessary, and so on.

Why is  there so much controversy surrounding the use of activated carbon? 
There are, I think, several factors which confuse the issue.  One is that activated carbon is peculiar stuff  - a kind of mystical material and many aquarists are uncertain about what it is or exactly how it works. Another is that most people do not realise that the term "activated carbon" is about as specific as the word "paint". There are many kinds of paint for many different applications, and you wouldn't expect interior latex wall paint to be entirely satisfactory for use on your car!  Likewise, some activated carbons offered for aquarium use are not very well suited for that particular application. Finally, I regret to say, there are several products on the market labelled "activated carbon" which are indeed carbon (coal) but are not "activated carbon". They are completely useless as water purifiers. An aquarist using one of these mislabelled products  is not likely to be favourably impressed by what he thinks is activated carbon. By covering the question asked most often about activated carbon we can perhaps shed some light on the subject.  We will discuss what it is, what  it does and doesn't do, the trace element question and other aspects of carbon filtration.

Why  is  activated carbon used  in aquaria?
We are all aware that the aquarium livestock generates toxic ammonia, which  is converted in steps to relatively harmless nitrate by bacteria living  in the filter bed. There are, however, a number of other contaminants generated in small amounts by the life process which can, over a period of time build up to a  high enough to affect the health of the inhabitants of the aquarium.
A slight yellow tinge to the water can indicate the presence of at least one such contaminant.  The most important function of activated carbon is to remove these impurities before they reach levels high enough  to cause distress or organ damage.
Activated carbon performs other important tasks in the aquarium as well, removing toxic dissolved gasses such as hydrogen sulphide and methane, which result  from imperfect water circulation.  It acts as a catalyst to quickly convert dissolved chlorine gas to relatively harmless hydrogen chloride.  It provides crystal clear water by removing minute suspended solids and colloids - those particles too small to be trapped by filter floss. It helps defend aquarium life on some occasions of accidental introduction of toxic substances such as pesticides,paint fumes,cigarette fumes and the like.

What is Activated Carbon?

Activated carbon, also called activated charcoal, is more involved in your life than you might suspect.  It is used  in the preparation of many products we use every day;  to remove those  impurities that cause an objec­tionable colour, taste, odour or health hazard from drinking water, waste water, foods and beverages (i.e. making sugar white instead of brown); to control air pollution (gas masks); and to separate/purify products in the chemical and pharmaceutical industries. The term "activated carbon" covers a family of materials made from carbon which have the ability to attract and hold certain substances on the carbon surface. This ability  is called "adsorption".  The adsorption process  is an example of what   is termed "chemical filtration", where certain dissolved substances are removed from the water.  Filter floss,  on the other hand performs "mechanical filtration" by trapping solid  particles suspended in the water.

The raw materials most commonly used to create the carbon are coal, peat, lignite, wood and nutshells.   None of these raw materials is pure carbon, although anthracite coal comes close. They contain unwanted hydrogen and oxygen as well. Those components are driven off by heating the raw material in the absence of air to produce a "char" (wood produces charcoal).  The char is then activated by exposure to an extremely hot gas, usually steam at about 1500 deg. F, which etches tiny passageways through each carbon particle.  The raw material selected, plus the manner in which it is activated, determines the characteristics of  the finished activated carbon product and its cost.  There are dozens of different kinds of activated carbon produced.  Of these, only a handful will be well suited to any particular application.

Conversely, no one carbon will do well in all applications.  For this reason, it is impossible to grade carbons, and terms such as "laboratory grade", ”research grade", "premium grade" and the like do not exist   in  the activated carbon industry.  Such terms are invented by the manufacturers in the aquarium trade to suggest,  or imply quality, because the real clue to a carbon's suitability for aquarium use - the specification  sheet  -  would  be unintelligible to most aquarists.  In discussing the following questions though we will  cover many of the items that are found on a spec.sheet.

 How does activated carbon work?
A particle of activated carbon is mostly air. It has thousands of tiny holes and crevices through which water can circulate. When water carries an organic molecule – a contaminant – into these narrow passages a short range attractive force between the molecule and the carbon will become effective and the molecule sticks. This particular method is called physical adsorption. The other kinds of adsorption also involved with activated carbon are of only minor importance to the aquarium.

 What type of activated carbon is best for aquaria?
The  effectiveness of an activated carbon for aquarium water purification depends on several factors which include total available surface area, pore size distribution, pore volume and particle size:

Surface area.   Carbons having more surface area  for impurities to stick to will obviously hold more impurities.  Interestingly enough, virtually all the useful surface area in activated carbon is along  the interior pores and not on what we think of as the outer surface has a negligible surface area because it is not  porous, and has no measurable adsorptive capacity.
(Although  it can provide mechanical filtration, ordinary coal does not remove dissolved contaminants.)
Wood charcoal is primarily a mechanical filtration medium with a slight adsorptive capability.  Higher on the surface area scale are the bone chars made from animal bones, and other surface activated carbons. These,  as the name implies, have an active outer surface covering an inactive carbon or phosphate core. Highest   in surface area are the totally activated carbons. These are porous throughout the carbon particle and a total area can range upward to approx. 1,000 sq. m per gram (300,000 sq. ft per ounce).  Surface area is a spec  sheet item  and  is always expressed in square metres per gram. For aquarium use, more surface area is not necessarily better,  because extremely high surface area implies a preponderance of extremely small holes or pores, too small for some of the larger molecule contaminants that we want to remove.  Look for surface area figures in the 500-900 sq. m/gm range.

 Pore size distribution.  Pore sizes in activated carbon are classified as micropores,  transitional pores and macropores (i.e. small, medium and large pores).  Small size pores are limited to the adsorption of small molecules, medium pores concentrate the  larger organic molecules typical of many aquarium  contaminants. Larger pores provide easy water access to the interior of the carbon grain, resist clogging, and also perform a  mechanical filtration function by trapping minute suspended solids to improve water clarity.
Most activated carbons have too much small  pore and not enough medium pore capacity to be  really effective for aquarium use.  What happens is that the  carbon becomes saturated with large  molecule  contaminants  in a relatively short time while still retaining  lots of unused space for small  molecules.   A good clue to favourable pore size distribution is a spec sheet figure called pore volume.

 Pore volume.   The combination of a relatively high  percentage of medium and large pores plus a high surface area results in a carbon which has a high pore volume - lots of empty space inside the particle. A good pore volume figure would be 1 to 1.5 cc (or millilitres) per gram. High pore volume carbons appear to weigh less - to have a lower apparent density - than other carbons made from the same raw materials.

 Particle  size.   The smaller the carbon  particle,   the shorter the water travel distance to the interior surfaces. There are several advantages to be obtained from using smaller particles. The activated carbon works faster, remaining effective in the modern outside filters, where the water flow rate is much  faster than the rate considered ideal  for carbon filtration. Useful lifetime is improved  with small particles since they are Less likely to clog on the outside before all available adsorption sites are occupied on the  interior surfaces. Particle size is indicated on a specification sheet by a notation such as "4 x 12 screen  size",  meaning  that  the product contains all those sizes which will fall through a screen having  four wires per  inch and not fall  through a screen with 12 wires per  inch,  giving a size range of approx. 1/4  to 1/12 inch.  (The gravel industry uses the same system, as in "6-20 silica".)

Economy.  Totally activated carbon is the kind recommended for main aquaria, and it is (naturally) the most  expensive form of aquarium carbon. On the other hand, it is by far the most economical kind to use when measured on a basis of cost per month of water purification service. A little goes a long way.  It has 5-10 times more capacity than bone char and  50-60 times more than charcoal, yet it costs about 2-4 times more.

Activated Carbon Article #2:

Activated Carbon
Filter medium extraordinary

 by Bob Straughan
From the Calypso Fish & Aquaria Club, London, England

 Activated carbon gets the water so clear that fish seem suspended in space! This was one of my early statements on this fantastic filtering medium, and decades later I am even more enthusiastic about the fabulous filtering qualities of activated carbon. In my opinion it is without equal in the aquarium field, and to do without it is to do without a sparkling clean aquarium where the water becomes invisible and the living jewels of the sea sparkle in water that is not only scrupulously clear but chemically and biologically clean. What more could be asked of a filtering medium?

Yet activated carbon is not well understood in the aquarium field - particularly in the salt water world. Improperly used, it can wipe out a tank of expensive fish overnight. Properly used, it can keep a tank full of fish in healthy condition for years without a single change of water. In fact, with the advent of the all glass tanks, a good undergravel filter with silica sand and a good outside filter that reaches all the way to the bottom with the siphon stem, it appears possible that a salt water aquarium could remain healthy and in good condition for a period of ten years without a single water change, provided, of course, activated carbon is used properly in the filter and good aquarium maintenance is observed at all times. Therein lies the solution to the successful use of activated carbon in the aquarium. You must know what you are doing! Otherwise you will have little or no success with the carbon.

Success with activated carbon depends upon several factors chiefly of which is the carbon itself. Like everything else, there is a great difference in carbons. Some are very cheap, others costly. Some are made of animal bones, wood, and various other materials. We use a product made from coconut shell, which we feel is consistently more pure and chemically inert than other products. It may or may not be the best, but I personally have tested it over many years in well over a thousand salt water aquariums under all types of conditions. It does the job and does it well, which is good enough for me. Until I find a product that works better, I am well satisfied with it. I have tried other brands of carbon of course. Some worked good; others were lethal.

Activated carbon is a powerful filtering agent. They used it in cigarettes, space ships, and deep sea submarines. It removes practically everything from the air, and in our instance, from the water. Because of its ability to extract gases, odours, fumes, etc., from the air, it can pick up poisonous substances from the air simply by being stored near them. In the case of chemical houses or pet stores, an opened case of carbon can absorb lethal doses of insecticides, paints, and dangerous chemicals, which could eventually cause problems in the aquarium. This sometimes causes unexplained failures with carbon when used in the aquarium. It also points out that activated carbon should be handled and stored with great care in air tight bags, especially if it is stored in a room with highly volatile substances. Otherwise it will be contaminated and unfit for use.

As pointed out above, there are many grades of carbon. Choose a known brand and one that is used by your local dealer if he is using it, or order a good quality carbon. The better grades of carbon will vary in price  per pound, depending upon whether it is cured or fresh. At the higher price it seems expensive, but it will last a long while. Contrary to popular opinion, carbon does not lose its efficiency after a few hours in the aquarium. Quite to the contrary, it improves vastly with age! Well aged carbon is completely safe to use, for it is neutralised by its constant use. It can be used over and over again, even for years if it is not contaminated with oils or dangerous chemicals. Those who would state that carbon is not an effective filtering medium should try it sometime. I don't know where they obtained their information, but it's a fact that carbon five years old will turn a dull, dingy, brown colored aquarium into a thing of sparkling clean water as clear as distilled gin. Well, perhaps it's not the carbon that gets the water clean when you place it in the filter. It must be the spirit from the great beyond! Or perhaps these people don't know what they are talking about. I'm inclined to believe the latter.

The safest way to use activated carbon is to cure it in salt water for a few weeks before placing it in the filter. Then rinse it well in fresh water. It is best to start it in the filter when the tank is first set up and the fish have not yet been added. Let the filter operate for a week or two with the water, and then add the fish, floating them in a container and introducing them gradually to the aquarium. Carbon filtered water is different from unfiltered water. Salt water fish cannot take ANY sudden change from one type of water to another. The same is true when they are being introduced to a carbon filtered tank or when their aquarium is to have carbon added to it for the first time. It must be done very gradually so that the fish can slowly become adjusted to it. If a tank has been set up for several months, the sudden use of carbon can prove disastrous. In this case, a small amount of carbon, say a teaspoonful to a tablespoonful, should be added to the empty filter once or twice a week, gradually building up the carbon until the filter is full. But the carbon should be aged before use. This is most important.

Many people write inquiring whether or not glass wool or nylon, should be used in conjunction with the carbon. This is a matter of choice. If you have a good filter, you can use just the carbon, but if the filter has wide slots in the bottom, a little nylon or orlon will keep the car­bon from passing through the slots. We don't recommend glass wool, as the synthetic floss is safer to use in the aquarium and easier to handle besides. A little of it placed above the carbon will help trap additional dirt and is easily removed when dirty, which will help keep the carbon clean longer.

We also get many inquires about resins for keeping the water clean. To date, we have not seen any resins that would keep the aquarium water clean, and we have tried some of them. The only time we recommend them is when aquarium water needs softening, in which case they probably do help.

We have used the activated carbon all by itself with nothing added to it for most of our experiments, and the results have been phenomenal to say the least. It will get the water unbelievably clear arid keep the fish in perfect condition. We have even reclaimed chemically coloured water almost the colour of coffee, which was discoloured by adding copper sulphate and sulfathiazole sodium to the same tank for disease control. We had to change the carbon a couple of times, but it did the job. It got the water so clear you couldn’t see it, and the water was perfectly healthy even though it was nearly two years old! We put in a large variety of both Atlantic and Pacific fish and they flourished in the peak of health and splendour.

Activated carbon can't do everything. It can't cure a sick fish. It can't keep an aquarium clean if you aren't using enough of it or if you overfeed or put some bad coral in the tank. Everything has its limitations. But if you use it correctly, a half pound to a pound for ten gallons depending upon other filtration, number of specimens, etc., and use it in a good filter so it can do its job proper]y, it will give you the cleanest water you have ever seen. You'll have to wash it when it gets dirty and dry it in the sun every now and then, but this is a small task and takes but a few minutes.

Use good carbon and use enough to do the job. Your reward will be the cleanest water you can imagine, as clear and sparkling as a mountain spring. The colours of your fish will be pure poetry.