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An
Article by Andreas Iliopoulos, John G. Reclos and George J. Reclos
THIS ARTICLE APPEARED IN THE JANUARY 2002
ISSUE OF FAMA
Preface
A lot of
us have probably already used a corner–box air-driven filter. Usually, you
will use aquarium moss and charcoal as media for this type of filter. Many
hobbyists have managed to keep their first fry tanks successfully using
this filtration scheme, which is still among the best choices for such a
tank – and not only.
Of
course, aquarium moss (a mechanical medium) is not responsible for this
success, as it can only trap big particles or waste. On the contrary, what
is most important are the invisible pollutants that remain in the water
giving it the characteristic yellowish color or an undesirable odor that,
in the end, can be transformed into lethal substances. There is only one
solution to this: the use of charcoal. Charcoal will effectively remove
organic wastes before they convert into pollutants that affect water
clarity, smell and safety.
Definitions
The use
of special manufacturing techniques results in highly porous charcoals
that have surface areas of 300-2,000 square meters per gram. These
so-called active, or activated, charcoals are widely used to adsorb
odorous or coloured substances from gases or liquids. Activated
charcoal or activated carbon is an amorphous form of carbon.
This means that it has no regular atomic structure, unlike the other forms
(allotropes) of elemental carbon: diamond, graphite, fullerenes or
nanotubes.
General –
How we ask for it?
Charcoal
is silken, black, shining, irregularly–shaped fragments of charred wood or
bone, with no further elaboration. This type of carbon is of limited use
in aquariums. It is good only for fresh water tanks, with a minimum of
fish load. It is sold as aquarium carbon or filter carbon. However,
charcoal has been replaced by “Activated Carbon” (AC for short) during the
last years.
Different
kinds of carbon can be produced which can then be used for removing
different kinds of impurities. The secret of AC power lies in its
elaboration. For example, when acids are used during the activation
procedure, the result is a carbon with an extremely porous structure. This
kind of carbon is mainly used for air filters. Different kinds of carbon
can be made if carbon is subjected to high temperatures and pressure.
It always
becomes a very porous medium, but the size of its pores depends on the
gases used during activation and the inorganic salts (copper, phosphates,
sulfates, silicates or zinc salts) that were added before the activation
procedure. Thus, we can now produce activated carbon with very specific
properties. Anybody can find special AC for aquarium use, which has been
activated at 2.000 ºC in vacuum, not washed with acids, etc. It is sold as
activated carbon or “super” activated carbon.
Function
AC works
in two different ways. It can remove organic substances by absorbing
them inside its sponge-like structure and/or by adsorbing them with
chemical bonds.
Absorption
is based on the vast number of pores. You can imagine it as a material
with too many pockets (very tiny pockets, the smaller the better), which
can be filled with small things (molecules). It could be referred to as a
very fine mechanical filter, which can absorb things the size of a
molecule. Thus, it is important to keep those pockets functional for as
long as possible. In this aspect, a good mechanical filtration is
essential before water reaches the activated carbon part of your filter,
otherwise carbon will be clogged very quickly.
The word adsorb is
important here. When a material adsorbs something, it means that it
attaches to it by chemical attraction. The huge surface area of activated
charcoal gives it countless bonding sites. When certain chemicals pass
next to the carbon surface they attach to the surface and are trapped.
Activated
charcoal is good at trapping other carbon-based impurities ("organic"
chemicals), as well as things like chlorine. Many other chemicals are not
attracted to carbon at all - sodium, nitrates, etc. - so they pass right
through it. This means that an activated charcoal filter will remove
certain impurities while ignoring others. It also means that, once all of
the bonding sites are filled, an activated charcoal filter stops working.
At that point you must replace the filter.
Adsorption relies on the polarity of the various molecules. Polar
molecules have two “poles” that differ in their affinity for the water
molecules, so one side of the molecule is hydrophilic (likes water) and
the other one is hydrophobic (dislikes water – likes lipids). When the
polar organic molecule approaches the polar surface of AC, it is attached
on it by its hydrophobic (lipophilic) side and thus is removed from the
water solution that contained it. However, carbon will remove not only
organic compounds but also inorganic ones. This is especially important.
The following list shows some elements / molecules that will be removed by
the use of activated carbon. You can see that it will remove both organic
and inorganic substances (data obtained by Greek Water Company).
Contaminant *MCL, mg/L
---------------------------------------
Inorganic Contaminants
Organic Arsenic Complexes 0.05
Organic Chromium Complexes 0.05
Mercury (Hg+2) Inorganic 0.05
Organic Mercury Complexes 0.002
Organic Contaminants
Benzene 0.005
Endrin 0.0002
Lindane 0.004
Methoxychlor 0.1
1,2-dichloroethane 0.005
1,1-dichloroethylene 0.007
1,1,1-trichloroethane 0.200
Total Trihalomethanes (TTHMs) 0.10
Toxaphene 0.005
Trichloroethylene 0.005
2,4-D 0.1
2,4,5-TP (Silvex) 0.01
Para-dichlorobenzene 0.075
Contaminant **SMCL
---------------------------------------
Color 15 color units
Foaming Agents (MBAS) 0.5 mg/L
Odor 3 threshold
Placement -
Utilities
Once we
decide which kind of carbon is suitable for our tank and our fish, we have
to decide about the place of the medium in our filtration system.
There are
many options. We can put it inside the chamber of an internal or a
canister filter, or in a chamber in the external power filter.
Or we may
have a specially constructed carbon chamber in our internal, self–made,
filter. We can even place it in the carbon chamber that we have designed
in our self–made sump.
We may
also have a layer of carbon in our trickle filter. We can also construct a
contact chamber and place it in – line with our system. We may put hose
fittings at both sides of a PVC section and place AC filled bags in it. We
can locate this pipe on the return of the tank so all returning water is
forced to pass through the carbon before it returns in the tank.
Alternative
utilities
Forcing
water to pass through a contact chamber containing bags of carbon is not
the best way to use it, as it is easily clogged from particles, the same
way as a mechanical filter does. So, much of the carbon becomes “isolated”
and some water ends up traveling between the bags. At the same time water
flow slows down. We may avoid this effect if we do not use media bags
(especially the ones with fine mesh size) or by using grate screens
between the bags. The whole idea is to use bags for carbon (because
handling it becomes easier), but to place the bags in such a way that
water is not forced directly through them. It must be flowing freely
around them, allowing enough contact time between water and the carbon’s
porous surface in order to remove the waste compounds from it.
We may
simply put AC bags in the sump and the organic compounds will be removed,
as water will be flowing over AC (through diffusion). This way, the water
will be kept clear and trace elements will not be depleted as quickly as
when we force water to pass through AC.
We have
to be careful and make sure that the bags cannot move freely in the sump
and be drawn up against the pump’s intake. We may use plastic baskets,
panels or egg crate diffusers to keep the AC bags in place (away from the
pump intake).
We may
even place the bags inside the tank, near the maximum water flow or behind
the rockwork.
In a tank
with an under gravel filter, we may bury bags with AC under the gravel
next to the airlifts. This method becomes very messy when the time for
replenishing AC comes.
Quantity –
Frequency of replacement
After
finishing with the installation issue we have to deal with the quantity we
must use in our system as well as the frequency of changes and the amount
of AC we have to replace in each change. The answers to those questions
are not easy since there are no recipes.
Different
tanks have different needs since there are many parameters (different
sizes, different animals, different stocks, different foods and different
ways of care) that define the need for AC changes and the overall quantity
of AC for a system. All the parameters mentioned earlier influence the
amount of the Dissolved Organic Carbon, which will be
present in our system (fatty acids, amino acids, organic acids, proteins,
carbohydrates, plant hormones, carotenoids, phenols, vitamins, etc). DOC
is the total of all chemical compounds that include the carbon element in
their structure. DOC affects growth negatively while it induces metabolic
stress and reduces disease resistance.
During
the 80’s and 90’s many studies were worked out and published on this issue
(Thiel, Moe, deGraaf, Hovanec, Spotte). Most of them suggest 36 ounces of
AC for each 50 gallons of water, or 500 g of AC for every 100 liters. You
have to start by adding 20 g of AC for every 100 liters of water on a
monthly basis till you reach the 500 gr. /100 liters mark.
This is
more or less a good ratio. This dose is suggested for reef aquaria but it
is tested (and works fine) in several kinds of aquariums and different
species. Of course, this figure is an average and should be used as such.
An overstocked tank will need more AC for the same volume.
Parameters affecting AC
performance
The adsorption process depends on the following
factors:
1) physical properties of the AC, such as pore
size distribution and surface area
The amount and distribution of
pores play key roles in determining how well contaminants are filtered.
The best filtration occurs when pores are barely large enough to admit the
contaminant molecule
2) the chemical nature of the carbon source, or
the amount of oxygen and hydrogen associated with it
The filter surface may actually interact chemically
with organic molecules. Also electrical forces between the AC surface and
some contaminants may result in adsorption or ion exchange. Adsorption,
then, is also affected by the chemical nature of the adsorbing surface.
The chemical properties of the adsorbing surface are determined to a large
extent by the activation process. AC materials formed from different
activation processes will have chemical properties that make them more, or
less, attractive to various contaminants. For example, chloroform is
adsorbed best by AC that has the least amount of oxygen associated with
the pore surfaces.
3) chemical composition and concentration of the
contaminant
Large organic molecules are most effectively
adsorbed by AC. A general rule of thumb is that similar materials tend to
associate. Organic molecules and activated carbon are similar materials;
therefore, there is a stronger tendency for most organic chemicals to
associate with the activated carbon in the filter rather than staying
dissolved in a dissimilar material like water. Generally, the least
soluble organic molecules are most strongly adsorbed. Often, the smaller
organic molecules are held the tightest, because they fit into the smaller
pores.
Concentration of organic contaminants can affect the
adsorption process. A given AC filter may be more effective than another
type of AC filter at low contaminant concentrations, but may be less
effective than the other filter at high concentrations.
4) the temperature and pH of the water
Adsorption usually increases as pH and temperature
decrease. Chemical reactions and forms of chemicals are closely related to
pH and temperature. When pH and temperature are lowered, many organic
chemicals are in a more absorbable form.
and
5) the flow rate or time exposure of water to AC.
The process of adsorption is also influenced by the
length of time that the AC is in contact with the contaminant in the
water. Increasing contact time allows greater amounts of contaminant to be
removed from the water. Contact is improved by increasing the amount of AC
in the filter and reducing the flow rate of water through the filter
Characteristics – What to buy? – What to care about?
Usually
good quality AC remains active for a period of about six months. After
this period organic compounds start to accumulate in the system as AC is
losing its activity. So we have to replace about 30% of it and at the same
time wash the rest with aquarium water. The reason is that AC works as a
biological medium as well as a chemical one. If we replace the whole
amount, the biological substratum of the system will be disturbed and the
denitrification potential of the tank will be seriously affected
(specially if we use a large quantity of AC). We should add the fresh AC
in front of the old material, so nitrifying and denitrifying bacteria will
colonize it quickly and the colonies that already exist in the old AC will
remain preserved. Rinsing 70% of the old AC with aquarium water reduces
clogging, while the biological substrate remains stable enough to remove
excess of organics for several months.
A good
and clever trick to determine when we have to replace the AC in our system
is to install in one side of the tank a piece of white plastic, half
colored with a yellowish, non – water soluble paint. When we cannot
distinguish the faint yellow part from the white one when we view it from
the other side of the tank it is time to replace the carbon in the system.
As
mentioned earlier, there are many ways to manufacture AC, therefore all AC
are not made the same. We shall choose AC for aquarium use only, with
small grains, dull black and as dust-free as possible. We have to rinse AC
with water to remove the excess of dust before using it. Some companies
use phosphoric acid to increase the carbon’s surface, because acid creates
more holes on charcoal. This AC is good for air filtration but is totally
unsuitable for aquarium use, even if it is thoroughly rinsed. It will
still contain ash and phosphates in high levels. If we use it we will
always wonder why we have algal blooms in our tank despite the fact that
we replace it sooner than the sales man told us.
We can
test our AC with a phosphate test kit. In our test vial we add purified
water until the marked level and we add the phosphate reagent as is
prescribed for doing a phosphate test. Then we put some AC grains in the
vial (5 or 6 are fine). If the color of our supplement shows a blue tint
or, even worse, becomes blue, then our carbon releases phosphates.
Needless to say, such carbon is not to be used in a tank.
AC has
another drawback: it ages. When this happens, some of the substances that
were absorbed previously will probably be released back in the water.
Some aquarists are relating AC
use with some strange, and sometimes unexplained effects like lateral line
disease or head erosion and other ailments. Therefore, it is better to
choose the carbon we use very carefully until new studies on this topic
are published.
Is it all good? Reasons to
consider using AC in your tank
AC
filtration does not remove microbes, sodium, nitrates, fluoride,
and hardness. Lead and other heavy metals are removed only by a very
specific type of AC filter. Unless the manufacturer states that its
product will remove heavy metals, the consumer should assume that the AC
filter is not effective in removing them.
As with
all known types of chemical filtration, AC removes useful substances
from the water (trace elements for instance) at the same time as it
removes pollutants. This effect can be prevented with partial water
changes and/or with simultaneously adding trace elements (e.g. iodine
deficiency in reef aquaria, is critical to the well being of soft corals).
However, this leads to a great uncertainty, since you can’t be sure how
much of the useful stuff is removed (unless you check for every single
substance) or how quickly it is removed. This is especially true for
planted tanks (removal of fertilizers, chelated iron etc.) as well as
special additions for the well being of the fish (like vitamins). In the
end, you might end up adding more and more vitamins, trace elements and
fertilizers until you saturate your AC with your own stuff.
Bacterial
growth:
When the water passes through the AC, some bacteria (primarily
heterotrophic) are trapped in the substrate, too. The problem is that
these trapped bacteria multiply prolifically in the warm, moist
oxygen-containing environment among the grains of AC. Because the AC is
loose, there is no barrier to keep any bacteria growing inside the filter
from coming out with the water pushed through each time the filter is
used. There have been extensive tests showing certain filters have
thousands more bacteria coming out of them than initially went into them!
Fresh activated carbon will
lower dissolved oxygen levels for a short period of time, and may, as
a result, lower your redox potential as well.
AC should be removed
each time you have to medicate your tank (otherwise all the medicine will
be absorbed by it). This may not be practical, easy or desirable.
There is a general trend to
simplify things. The “Keep it Simple” approach has become the
principle many aquarists believe in. In this context, the addition of one
more (largely unpredictable) factor in a tank should be avoided.
Epilogue
Some
aquarists use Activated Carbon constantly, while others use it
periodically. Some don’t use it at all. As we already discussed, there are
pros and cons for using it – definite conclusions or suggestions can’t be
drawn by us.
It is
evident that in the end, the only person to decide if a particular kind of
AC is beneficial (and to what extent) to any particular system is
definitely the hobbyist himself. Your personal observations concerning the
appearance of your tank and the well being of your fish coupled to the
knowledge of your system are the true guides for that.
The only
worthy indication for the proper use of AC is the appearance of your water
and inhabitants. The organisms kept in aquariums are more sensitive in
water chemistry mishaps than any electronic gadget, so it is better to
spend some time observing your system and the captive life kept in it,
rather than playing the chemist with exotic instruments.
There are
some of the so–called hobbyists that do not understand even the basics
(not even what pH is) and in which ways they affect water chemistry and
aquatic life, pro rata. On the contrary, sometimes their tanks are fully
equipped with electronic equipment. Almost all of them believe that a
well-equipped tank does not require any care; they do not even perform
partial water changes. Take our word for it: the most important equipment
for a successful tank is you.
There is
no kind of chemical filtration (activated carbon, protein skimming, ozone,
phosphate adsorbing media, etc), nor any other kind of filtration that can
miraculously replace the need for your personal care for a tank. The more
sophisticated the system, the more experienced the aquarist it takes. The
more personal our involvement with our tanks, the more experienced we get.
The more we inform ourselves, the better we use our experiences - on a
practical level – for the better care of our tanks and fish.
Literature
MERCK
Index, An Encyclopedia of Chemicals, Drugs and Biologicals,
11th Edition, Merck & Co Edtns, USA, 1989
Thiel,
The Marine Fish and Invert Aquarium, Aardvark Press 1989
Moe,
Marine Aquarium Reference: Systems and Invertebrates, Green Turtle
1989
deGraaf,
The Reef Aquarium vol.1,J. C. Delbeek - J. Sprung 1994
Hovanec,
All about Activated Carbon, Aquarium Fish Magazine 1993
Spotte,
Seawater Aquariums: The Captive environment, Wiley - Interscience
1979
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