|Activated carbon article #1:
Activated Carbons / Charcoals - The Rundown
by Richard M. Greenfield
First published in the (now closed) British Marine Aquarists Association
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.
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.
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
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
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
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.
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.
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:
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.
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.
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:
Filter medium extraordinary
by Bob Straughan
From the Calypso Fish & Aquaria Club, London, England
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.
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 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 couldnt 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
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.