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We find it much easier to introduce the biological
filteration process after we have delivered
a proper understanding of the biochemical
process that occurs in aquarium systems.
So we will start off by looking into the
biochemcial process and the importance of
different alges and bacteria, and live rocks.
Then we will come back to the biological
filteration issues and introduce the basic
principle of protein skimmers.
Generally speaking, decompsition in any aquarium
system refers to the chemical reactions that
convert organic material into inorganic material. The chemical reactions, however, do not
take place automatically. The chemical reactions
require different types of bacteria to break
down the organics into inorganics in a step-by-step
fashion. The process of the chemical breakdown,
however, also produces toxic by-products.
Usually these intermediate by-products will
be handled by the different bacteria in the
next step of the chemical reaction. But if
the amount of these toxic by-products exceeds
the level that your tank is able to handle,
the accumulation of these by-products must
be removed manually. The removal of these
undesired by-products represents the biological
filteration process.
The chemical organics that we want to remove
from our tanks come from overfeeding, decay
of dead algaes and dead corals, together
with the natural metabolism of the living
creatures. The major organics are Ammonia
(NH3), Ammonium (NH4+), Urea, and uric acid.
Common to all these organics is the presence
of the Nitrogen (N) atom, and hence, they
are usually referred to as the nitrogenous organics. The breakdown of the nitrogenous organics
is generally described in establishing the
cycle for a new tank. The nitrogenous cycle
involves three stages: Mineralization, Nitrification,
and Dissimilation. These three stages occur
in the order as described because the next
stage cannot happen without the end products
from the previous stage. If the nitrogeneous
cycle is successfully established, Dinitrogen
Oxide (i.e. Laughing Gas) and Nitrogen gas
will be produced at the end and the process
is called Denitrification.
What do we mean by "If the nitrogenous
cycle is successfully established ..."?
Denitrification is not necessary a-must.
There is always a possibility of Nitrate
Reduction. The Nitrate Reduction represents a failure in establishing the
nitrogenous cycle because the end-products
are Ammonia (NH3) and Ammonium (NH4+) - same as what we started with. However,
same as the situation of heavy metal elements,
the chance of Nitrate Reduction is very low.
If you do everything correctly, Nitrate Reduction
barely occurs and you should not be worrying
about it.
Back to Table of Content: alt-qAlgaes
As we have mentioned above, many different
types of bacteria and organisms must be present
in order to set up a successful denitrification
process. Therefore, we want to introduce
a few terms used to describe these bacteria
and their living conditions. These terms
will become very useful in the following
discussion of the three stages of the denitrification
process: Mineralization, Nitrification, and
Dissimilation. They also help you to appreciate
the usefulness of live rocks (besides its
aesthetic interest) later on.
Algaes are always present in your tank. Algaes
are simply a type of plants that live in
the water. Same as other plants, algaes are
capable of doing photosynthesis. They convert
inorganic material, water, and carbon dioxide
molecules into sugar in the form of glucose.
So we see that some algaes are desirable
because in the process of supporting their
own living, they eliminate some undesired
inorganics, mainly nitrogen and phosphrous,
from the water. This immediately fits into the goal of the
bio-filteration proces.
However, as you know that not all algaes
are welcomed in the tanks. This is paricularly
true with the green algae. Green algae can usually be found under
the bases of corals. They are bad because
they weaken the skeleton of the stony corals,
and hence, the bases become soft. This eventually
destroys the bases and kills the corals.
There is another reason for which we want
to keep the growth of algaes under control.
We said that algaes are capable of doing
photosynthesis and they convert inorganics
into organics. The problem comes in when
the algaes decay. The inorganics that were
stored inside the algaes' cells will be released
upon the death of the algaes. For this reason,
algaes are also known as the "nutrient bombs". When the "nutrient bombs"
explode, they release excess amount of nitrogenous
compounds into the tank. Unlike the ocean,
there is comparatively much weaker current
and a much smaller volume in the tanks. The biological system cannot handle the "nutrient
bombs" in a tank as easily as in the
ocean. This gives another good reason for you to
set up a good bio-filteration system.
Bacteria and their Living Conditions
Similar to the situation of the algaes, there
are numerous kinds of bacteria. However,
we will only talk about four types of bacteria
here. In fact, the four types represent only
two groups of bacteria. The first group is
aerobic and anaerobic and the second group is the heterotrophic and autotrophic bacteria. Aerobic bacteria require oygen
to live; whereas anaerobic bacteria do not.
On the other hand, we can also categorize
bacteria according to how they generate energy
to support their only living. If the bacteria
gain the energy by consuming the glucose,
they are heterotrophic. On the other hand,
bacteria that can generate energy for their
needs without consuming glucose are autotrophic.
For example, nitrifying bacteria gain the
energy by oxdiating inorganics (not by consuming
glucose), hence they are autotrophic. Nitrifying bacteria, which is involved in
the Nitrification process, is also aerobic.
Bacteria involved in the Dissimilation process,
however, is anaerobic. (In general, nitrifying bacteria is called
chemo-autotrophic bacteria. There are other
types of autorophic bacteria, but they do
not clearify the discussion any further.
So we omit them here.)
Wave-Making Power Bar
As you can imagine, the distribution of oxygen
in the tank is closely related to the steam
of the current. For a reasonably large tank,
there is a need to have more than one return
or power-head to pump water from the sump
back to the tank. The idea is to generate
a resultant steam that can eliminate the
dead zone (area with a low oxygen level or
anaerboic area) as much as possible. In the
old days, this requires you to locate the
best spots in the tank for your power-heads
so that one steam is opposing to the others.
This makes the distribution of oxygen in
the tank more evenly.
Recently, there is a product in the market
that can reduce your time to locate these
spots greatly. The product is simply a power
bar that has a built-in micro-controller
which can provide power to a particular outlet
in a pre-determined phase. By providing each
outlet power at a different time, this essentially
creates a cycle of the water flow in your
tank. The idea is to simulate the wave motion
in the ocean in your tank.
Below are two pictures of the same product:
the Natural Wave Multi-Cycle Pump Timer manufactured
by Aquarium Systems. The picture on the right-hand-side
shows the power cycle that each outlet has.
Note that this individual power bar has only
3 timer outlets. The other oulets are regular
ones. On the left picture, you can see that
this power bar has a knob to adjust the cycle
frequency.
Back to Table of Content: alt-q
As we mentioned above, denitirfication process
involves three stages: Mineralization, Nitrification,
and Dissimilation. These three stages require
the aid of different micro-organisms. Different
types of bacteria are responsible for a different
stage in the whole chemical cycle.
Mineralization
In the microscopic world, a giant Protein
molecule is a huge collection of well-formed
segments of molecules. These segments are
usually called amino-acids. In this stage, the amino-acids will be
reduced by the heterotrophic bacteria into
inorganics. The heterotropic bacteria make
use of the carbon atoms in the organic amino-acids
in the photosystheis process to support their
own living. This coincides with the first
step to break down the organics in your tank.
The end products are ammonia (NH3) and organic acids. Immediately, we see that these chemical
products must be handled in the coming steps
because none of them is desirable. Organic
acids is going to drive your buffer capability,
and hence, pH level down, if not properly
taken care of. Your pH level will soon be
low once the buffer capability is exhausted.
(If needed, please refer to the MoreChemical
page to clearify this point.) Although itself
is not toxic, the ammonia can transform easily
with water molecules into ammonium (NH4+), which is toxic in this ionic form. A certain
amount of ammonia can be handled automatically
in your tank by algaes. (Remember that algaes
are desirable because of their capability
of making use of nitrogenous molecules to
produce their own food.) But the majority
of these ammonia and ammonium products must
be taken care of in the Nitrification stage.
The nitrification process is to oxidize the
ammonia (NH3) and ammonium (NH4+) molecules into nitrite (NO2-) and nitrate (NO3-) respectively. Each chemical reaction involves specific
bacteria and heterotrophic bacteria. It has
now been widely known that heterotrophic
bacteria are good for aquarium system because
they can convert the amino-acids directly
into nitrite and nitrate by-passing the steps
of producing the toxic intermediate products.
Yet again, the good algaes in your tank can
take a certain amount of these nitrogenous
organics in the water and convert them into
harmless inorganics. Therefore, the good
algaes are really sharing part of the work
load for your bio-filteration system. Although
we advice against keeping any excess amount
of algaes (remember the "nutrient bomb"
issue), a healthy portion of algaes must
be present in your tank.
There are differnt test kits for you to test
the nitrite and nitrate molecules. Nitrite
molecules are extremely toxic. You can use
the test result to estimate the Nitrification
process in your tank. Although they are unwelcomed,
the ammonia and ammonium levels should not
be zero. They are the food for algaes in
your tank. Only the excess amount of these
molecules must be removed.
Dissimilation
As we mentioned in the prologue, there is
a finite, but very low, possibility for the
nitrogenous cycle to go wrong. That is, the
result of Nitrate Reduction. If the denitrification
process is succefully established (in most
cases, you will), the end products of this
stage are Dinitrogen Oxide (N2O) and Nitrogen (N2) gases. Because of their gaseous forms,
these end-products escape by dissolving from
the tank to the surounding air. (The dissolving
rate depends on the surface of the tank.
The larger the surface area, the better the
result. This is also one of the reasons why
we recommend a wide tank.)
There is one special condition required for
the dissimilation process. The bacteria involved
is of the anaerobic type. These bacteria
live only in the environment of oxygen deficiency.
This posts a very special constraint when
you set up your denitrification filter. (We
will come back to this point in following
section in establishing denitrification filter.)
So now we have done all the introductory
work and the rest of the biofilteration discussion
is quite straight forward. However, we want
to point out a few points that you want to
be careful in setting up your nitrogneous
cycle.
In general, Mineralization is not a major
concern. Make sure that you have the proper
bacteria to kick off the cycle if you are
setting up a new tank. The only potential
problem is to limit the growth of algaes.
However, controlling the growth of algaes
in your tank can be difficult. There are
a few factors that are closely related
to
the growth of algaes, for example, salinity
and the lighting system in your tank.If
you
have an algae problem, it is best to consult
with someone who had similar experience
before
and ask them how they fixed the problem.
Nitrification and Dissimilation are similar
yet different. The living condition for
the
bacteria involved in this two stages is
high
temperature. The requirement for these
stages
is different in that nitrifying bacteria
is aerobic, whereas bacteria in dissimilating
process is anaerobic. Together, these living
conditions provide specific guideline for
setting up your denitrification filter.
Back to Table of Content: alt-q
It is about time to introduce live rocks.
On the MoreLighting page, we mentioned that
daylight system is critical if your tank
has live rocks. We also mentioned that live
rocks are the biological filter in the ocean.
Now, let us look at the usefulness of live
rocks more closely.
It needs no introduction to how wonderful
the live rocks can decorate your tank. It
is the simplest and most effective way to
make your tank look like the ocean scenes
that you see on TV. Live rocks are erosive-looking
rocks that are found in natural ocean. Live
rocks are porous and usually have thousands
of holes scattered throughout the entire
structure. The porosity is actually an essential
attribute for the live rocks to act as biological
filters.
The erosive-looking surface provides a much
larger surface area than a smooth surface
for micro-organisms to live on. Surface area
is actually very important in deciding which
filter substrate to use in the denitrification
filter. The idea is always to provide the
largest surface area for bacteria to settle,
so that the bacteria will not be washed away
by the constant current entering the filter.
This explains why the filter substrate should
be fine and perferrably has a rough surface.
Since the holes are scattered throughout
the entire structure, you can image that
bacteria living inside the rock have a very
different living condition than those living
on the surface. For those bacteria living
on the surface of the rocks, they have bright
light and sufficient oxygen. For those bacteria
living inside the rocks, however, there is
no light and a low level of oxygen. Therefore, we have both aerobic and anaerobic
bacteria living on the same piece of live
rock. Live rocks are in fact an excellent bio-filter
because the nitrate produced in the Nitrification
stage is handled immediately in the same
piece of live rock. This greatly reduces
the amount of excess nitrate in the water.
Our experience has also shown that using
live rocks to set up the biological cycle
is a lot quicker than using the other bio-filter
products that you can get in the market.
We strongly recommend the use of live rocks
in any aquarium system.
Back to Table of Content: alt-qBefore we leave for the discussion of bio-filteration,
we want to bring up another jargon used in
aquarium system. The Redox potential is another
measurement that is similar to pH in nature.
They both indicate the general well-being
of the tank. pH measures the acidity or basic
level in your tank. Redox potential measures
the ability for the chemical particles to
react with each other. Redox stands for two processes: reduction
and oxidation.
You may have noticed that the chemical reactions
in the three stages of denitrification is
really a series of transfer of electrons
from one group of elements to ions. The originally
neutral elements donate electrons to the
ions so that the ions now become stable.
On the other hand, these originally netural
elements are now ionized because they have
lost their electrons. The originally neutral
element is called the reducing agent because it reduces the active ions to its
stable form. The final stable product is
called the oxidizing agent because it makes the neutral elements unstable.
Redox represents the process in which electrons
are attracted and transferred to the positive
charges in the water. (It is the simplest way to explain how your
battery works. But we are not interested
in getting into the details here.) What you
want to know about the Redox potential measurement
is that it has the unit of voltage. For chemical
reactions to occur in the tank, there must
be a certain level of Redox potential for
the electrons to be transferred. Since the
chemical reactions take place because of
the bacteria working on the inorganics, it
indicates how well the bacteria are doing
their work.
Unlike, other measurements like pH, salinity,
etc, there is no simple tools to measure
the potential. You have to meausure the potential
with a delicate electronic meter. Consult
with your local pet shop with the Redox meter.
However, you need to pay more attention to
the Redox potenial level if you also use
an ozonizer. Ozonization pumps up the Redox
voltage significantly. Why use Ozone? Ozone
is usually used because it breaks down organics
directly without all the toxic intermediate
by-products produced in the denitrification
process. However, ozone has the drawback
of being toxic itself. Ozonizers are generally
safe to use. Again, consult with your local
pet shop if you are interested.
Here is a picture of a Redox Controller.
It is the same idea as using the pH controller
(introduced in the MoreChemical Page) in
that a controller, unlike meter, can control
the Redox level.We have this particular controller
in stock. Please contact us if you are interested.
Back to Table of Content: alt-q
Biological filters serves the same purpose
as mechnical filters in that they are designed
to remove unwanted material from the water.
Biological filters, however, use bacteria
and micro-organisms to achieve that goal.
We mentioned that live rocks are excellent
bio-filters because they have a erosive-looking
surface and thousands of holes scattered
throughout the entire structure which are
perfect for the bacteria to live. These gives
a huge area for micro-organisms to live and
a living conditions suitable for both aerobic
and anaerobic bacteria needed in the denitrification
process.
In this section, we want to outline the importance
of three types of filteration system: bio-filters,
denitrification filters and protein skimmers.
Bio-Filters
(with Image Map Feature)
Bio-filters are quite easy to understand
because they all serve the simple purpose:
to provide the living conditions for bacteria
to process the denitrification cycle. Bio-filters
are to provide the living conditions for
bacteria to process the nitrification stage,
whereas the denitrification filters are to
provide the living conditions for bacteria
to process the dissimilation stage. The distinction
is quite obvious when you see that constant
water flow is encouraged in bio-filters,
but constant water flow is discouraged in
denitrification filters.
On the left, we have two bio-filters from
different manufacturers.Click on each box to see what is inside the
box.They are both fluidized bed bio-filters.
A fluidized bed filter has a chamber filled
with a fine filter media. The inlet is usually
connected to a power head (with a pre-filter
to block mechnical waste from entering the
filter). There is an inlet for the water
to flow into the bio-filter so that the water
pressure will lift the fine particles up
and the filterbed increases in volume. This
is the fluidized bed. The filter particles remain in a constant
mixing motion as long as the bio-filter is
running.
The fine filter particles are where the bacteria
colonized. Therefore, the finer the particles,
the more surface area the total filter-bed
can have in a given volume. The constant
water motion within the chamber is critical
because it ensures the availability of oxygen,
and ammonia, or the foods for the bacteria.
The rapid water motion is also good for keeping
a thin bio-film formed on the inside layer
of the chamber. This is because the filter
particles also brush the inside layer of
the chamber constantly. (Note: A thin bio-film
is better than a thick bio-film since it
is easier for the bacteria to exchange the
organics and the inorganics with a thin bio-film.
This is really the surface area argument.)
The bio-filters are very simple to use. Connect
the inlet to a power head (and the pre-filter)
and the outlet to another filteration unit,
such as the denitrification filter, or back
to the sump. The only thing that you will need to adjust
is the current flowing into the bio-filter.
With the MERLIN product, the water-flow to
the chamber can be adjusted mechanically
by varying the Flow Regulator. The Flow Regulator
has a Regulator Pin connected at the bottom.
Turning the Pin in different directions can
raise or lower the Inlet Tube, thereby varying
the opening between the Flow Nozzle and the
Deflection Plate. The larger the opening
between the Flow Nozzle and the Deflection
Plate, the larger the flow rate and the higher
the level of fluidization. The appropritate
level is anywhere between the marked levels
shown on the bio-filter.
The QuickSand Filter has a flow restrictor
which must be inserted into the filter's
outlet hose before set-up. When you are ready
to plug the QuickSand bio-filter in your
system, place your finger over the outlet
hose opening. Fill the chamber with water
and let go of your finger once the chamber
is purged of air. Let the water running for
an hour and turn the adjusting bolt (next
to the blue inlet) to adjust the water flow.
The fluidized bed should be wihin several
inches of the top of a vertical filter.
Although, it does not take long to install
a bio-filter, it takes a much longer period
for the cycle to mature. Setting up a tank with a new bio-filter can
take anywhere between 3 to 6 weeks. The period is determined by the initial
amount of biological load in your tank. So
to speed up the cycle, you can add a small
amount of detritus on startup. As we mentioned
in the biological function of live rocks
section, adding live rocks to your tank is
always an excellent choice to set up your
cycle.
Denitification Filter
Denitification Filter is designed to break
down the organics in the tank that the algaes
cannot handle. There are two conditions that
these filters must satisify in order to function
properly: the anaerobic living condtion for
the dissimilating bacteria and a low current
flow. The low current flow is needed to prevent
the bacteria from being washed away and to
provide enough time for the bacteria to work
on the organics. The proper set up of such
a filter requires an anaerobic area for the
bacteria to live. This anaerobic area should
draw your attention when you use your denitrification
filter because the effluent water is low
in oxygen. That is, you never connect the outlet of
the denitrification filter directly back
to the aquarium because of the low oxygen
level in the output stream. The water flow should be deliberately limited
to provide the time that the bacteria need
to decompose the organics in the water.
Picture of a Denitrification Filter
Here is a denitrification filter from Aqua
Media. It is all that you need for maintaining
the denitrification cycle in your tank. The
filter has a similar design of the Calcium
reactor (also from Aqua Media) discussed
on the MoreChemcial page. The bio-balls are
where the bacteria live. We have this particular
unit in stock. Please contact us for the
details of setting up the denitrification
cycle in your tank using this excellent system.
Back to Table of Content: alt-qProtein Skimmer
Protein skimmers are so critical that every
saltwater aquarium must have one. The protein
molecules that concern us here are the same
proteins generated from dead algaes and corals,
and regular metabolic behavior. The whole
point of bio-filteration is to remove these
protein molecules in the water. The protein
can be removed by algaes through their photosynthesis
and bacteria through the denitrification
process. However, nitrification (the second
stage of the denitrification process) usually
happens in a much faster rate then the denitrification
process. That is, the tank produces more
than it can clean up. So, there are generally
more protein in the water than these micro-organisms
can handle. This introduces the need of the
protein skimmer.
Pictures of a Protein Skimmer
Here we have shown an inexpensive protein
skimmer from Lee's Aquarium & Pet Products
just to illustrate the basic principle described
in the following discussion. Please click on the left picture to see the
full size of it. The terms used in the following discussion
correspond to the ones shown on the full
sized picture. The right picture is taken
in our store. It shows the simple protein
skimmer at work. The bubbles is formed in
the contact chamber and the waste material
is in the collection cup. The waste should
be cleaned regularly.
A protein skimmer is basically a tube, called
contact chamber, with a cup on the top to
collect the waste which you must remove regularly.
The contact chamber has an air stone sunk
at the bottom and is a place where you normally
see a lot of bubbles rising to the collection
cup (see the right picture above.) The usually
electrically charged amino- acids molecules
adhere to the air bubbles, by which these
charged molecules can be brought to the collection
cup at the top. When the air bubbles reach
the top of the foam riser tube, they come
into contact with the air inside the collection
cup, and hence, these bubbles form into foam.
You may notice that not all the foam formed
have the protein molecules adhered. You are
right. There are two types of foam here:
normal and protein foam. We only want the protein foam to be collected
in the collection cup and the normal foam
to be returned to the aquarium. The normal foam can be quickly broken up
and to be returned through the return tube.
They are easily recognized as the steam of
bubbles of identical size going back to the
aquarium. To see the bubble stream clearly. The waste
that we want to remove is a brownish protein
liquid (after settled) is called adsorbate.
So what can lower your protein skimmer's
ability to clean up the water? The basic
principle behind the protein skimmer is that
the water surface must be electrically charged.
However, if the food that you feed to your
corals and fishes contains fat, the left-over
food in the contact chamber is going to form
a layer that can break the foam easily. This
lowers the probability for the protein foam
to be collected. For this reason, the contact chamber should be cleaned regularly.
If you want your skimmer to work at its peak
efficiency, use air stones that can generate fine air
bubbles. The finer the air bubbles are, the larger
the probability for the protein molecules
to be stuck on the bubbles. The air stone
should also be kept at the bottom because
this ensures that the air bubbles have the
maximum amount of time to come into contact
with the protein molecules. This again increases
the probability for the protein molecules
to be collected.
One final note of choosing your protein skimmer
is that the bigger is not necessary the better.
Check the capability of the protein skimmer
before you purchase. The capability is usually
quoted as the number of gallon that the skimmer
is good for.
Back to Table of Content: alt-qOn this page, we have explained the bio-decomposition
process in the tank, the significance of
algaes and live rocks, before going into
our discussion of the bio-filteration process.
From our experience, we find that live rocks
and a good denitrification filter, a good
protein skimmer (not necessary expensive),
and a sufficient water movement are three
big factors that can easily give you a successful
aquarium system. There is a fair amount of material on this
page, we hope that you find the information
useful.
Back to Table of Content: alt-q
© Wai's Aquarium Ltd, 2000, 2001. All rights
reserved.
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