EVER WANTED TO KNOW
ABOUT FILTERS BUT WERE NEVER TOLD.
By Jim E. Quarles
BY Jim E. Quarles My good friend Walter at Discus Page Holland has
asked me to write this and provide it for his website. I agreed to do so
because it is a subject that comes up often when newcomers join our hobby.
And I feel it is important that they get the basics right at the start and
learn more as we all do when we progress into the hobby.
Before we get into the different kinds of filters we should clearly
understand the purpose of any filtering system. Basically a filter does
one of three things. 1. It removes solids from the water. 2. It provides a
surface area for bacterial growth needed to change chemical compounds from
one to another. 3. It can be used to induce chemical compounds to the
water you are filtering as well; this in turn will alter the chemical
nature of the water in many different ways plus it can aid in increasing
the oxygen content of the water by rippling the surface area on its
Filters do one or all the above things. It depends upon the design of
the filter and what you wish it to do.
It would be very helpful to you, the reader, to read the articles on
Discus Page Holland with the titles "Nature's Wonders 1 through
4". These explain in great detail just what bacterial filtration is
and how it works.
DIFFERENT TYPES OF FILTERS
FOR THE HOME AQUARIUM
AND HOW THEY WORK.
Let us first take a look at the good old under-gravel filter, this one
has been around a very long time and has earned the name." The filthy
demon filter. It generally is the first mistake a new comer to the hobby
makes, and the favorite the L.F.S. ( Local Fish Store) likes to sell you.
I think the reason this is done is that they just don't know any better,
and 2. It is a high profit item for them.
The principle way this filter works is to place it in the bottom of
your tank, and cover it with gravel. Then either with the use of water
flow or airflow you cause the water in the tank to flow through it. In
theory this sounds good. But in actual practice it leaves a lot to be
desired and in the end can wind up being worse then no filter at all. The
water passing though the gravel then allows certain types of bacteria to
grow on the surface area of the gravel. In theory this works pretty good,
but in practice, it becomes a nightmare for the discus hobbyist.
It does not take long before the pores though which the water flows
start to clog up with left over food and fecal matter from the fish. This
turns the filter into a big filth collector. This in turn invites all
kinds of harmful results. Diseases find a great place to grow and multiply
plus this type of environment is favorable to a great many parasites, and
allows the build up of harmful chemical compounds as well.
Anyone who has used such a filter for a few months and then had to take
the tank apart will know by the rotten egg smell that something is not
right in such a setup.
A lot of new hobbyist get started with this type of filter, and are
told to keep the gravel clean buy vacuuming the fecal matter and other
solids out by washing the gravel as they make water changes. Again in
theory this sounds good, but is not effective or practical for long term
use. All kinds of harmful substances are gathered under the filter plate
and these are not removed that easily. Some with say use reverse flow
power pumps to flush the gravel from bottom to top. Again this sounds good
but rarely works well. No the best way to handle this type of filter is to
not get involved with it. Just let the uninformed learn the hard way.
Remember this filter is deadly to discus in the long run. And the longer
it is in operation the worse the matter becomes.
THE DIATOMACEOUS EARTH FILTER.
This filter is rarely used in the average fish room. But it offers some
very special advantages for fish shows or if you need to filter the water
to what is often called a shine.
Diatomaceous earth is a powdery natural material that can be found in
different grades of pureness. It was formed almost entirely from the
skeletons of diatoms, which lived in the seas, and their skeletons were
deposited on the sea floor during the Cenozoic era. The material used in
filters is made up almost entirely of silicon dioxide or silica. Because
it is so fine it is often used in filtering chemicals and in special
applications where purity is required in the final product.
This filter offers the advantage of removing extremely small particles
from water, in fact it is said to polish water when used in fish shows, it
makes the water appear to sparkle or shine. Most bacteria are filtered out
of water using this system.
The disadvantages however, in general, reduce its usefulness for long
term use in the home aquarium. The pores, which the water flows through,
are so small that they clog quickly and the water flow is reduced below
acceptable levels. This requires frequent cleaning and replacement of the
filtering material: the D.E. earth. While this is not very expensive it
becomes a somewhat nasty chore and must be done all to often for most
I would not consider these types of filter a biological unit, in that
it does not operate through the use of a bacterial build up on the
filtering media. It should always be considered a filter to remove solids
only and then on short-term bases between cleaning and recharging with D.E.
Now we will look at one of the most useful of all the powered filters.
This filter offers many advantages and a few disadvantages as well. But
over all it will always play an important part in tropical fish keeping
This filter works within a closed container that is pressurized by the
internal water pump that causes the water to be forced through whatever
media is used. Lots of different things can be used within this type of
filter to treat the water playing though it. In addition it generally can
remain in the system long enough to be considered a low-grade biological
filter system as well.
One of the limitations is that the capacity is fairly small and it can
not hold a lot of desirable media at one time, such as peat moss. Most of
the canister filters are used with activated carbon and some type of floss
to catch and hold solids as the water is pumped through it. However they
do allow a very large water flow when maintained properly.
When shopping for this type of filter you will find a large number
offered for sale by several different companies and they come with a wide
selection of sizes and water treating capacity. I have in the past used
selected models made by most companies and found them all to be about the
same as far as dependability is concerned. Just bare in mind the different
features that each will perform based on size and power rating.
When we speak of power filters of course it includes the canister
filters but generally when you hear the term power filter you will find
people are referring to a filter that is an open system filter, in that it
is not operated within a sealed container and is not pressurized.
These types of filters are found in a very wide range of configurations
and sold by a large number of manufacturers, each offers it's own features
and most are rated in gallons per hour of water exchange. Do not confuse
the powered types with the air operated ones which will be explained as we
go along in considering all the different types of filters.
"In the beginning there was dirty water on the face of the
aquarium," and someone said, let there be filters! And it became so.
And everyone keeping fish said this is good. Now let there be different
kinds and it came to pass there were many made. Some good and some not so
good. And the voice said " Gees, they are never satisfied ".
When the outside box filter came along it was powered by air flowing
through an up lift tube that pushed the water into the box as the air
escaped to the top of the water. These filters are still in the hobby and
are still sold in great numbers worldwide. They for the most part are
designed to hang on the outside of the aquarium and air pump water back
over the edge of the tank after it flows into the box via a siphon tube.
The water is passed though some kind of media before being returned to the
In a way this is still a power filter by definition since is it powered
by airflow. But as now currently applied when you speak of a power filter,
this refers to one that is powered by an electric motor, which operates a
pump to lift or send the water into the filter box. You will find quite a
few arrangements of the principle when shopping for filters. All kinds of
cute sales gimmicks are added to increase your desire to own the best of
the best of the best. Example: cute little wheels that spin around as the
water flows over them. While I am sure this does provide additional
surface areas for the bacteria to grow on I would not bet the family farm
that it works as well as advertised and the add on cost should be
considered when comparing effectiveness of the filter and what you expect
it to do for the tank. Just because a manufactured item makes super claims
about a product does not make it a true statement of fact.
LET'S REVIEW A BIT
Just how does a filter work, and what are the most important features
we should look for in buying or even building our own?
Other than the removal of solids from the water, the filter should be
designed so that it offers the largest surface area possible for
nitrifying bacteria to attach themselves to for they are the basic working
staff or work horses of the biological filter.
When you study and ask questions about these bacteria you will find
that for every question answered two more questions will arise as a
result. For these are truly amazing organisms. And how they perform in the
filter depends upon its design and the use you the hobbyist make of it.
Once again for a more detailed explanation I refer you to the articles
"Nature's Wonders 1 through 4" located on the Discus Page
Holland web site.
CENTRALIZED FILTER SYSTEMS.
This type of filter offers the hobbyist who keeps multiple tanks the
advantages of using one or more central filtering systems that provides
proper filtration for a group of tanks. A system of this kind can be
designed with adjustable flow rates to each tank independently. A central
filter provides a larger volume of water though one set of media. And of
course if the system is properly designed each tank can be removed from
the system through a set of valves without interrupting the flow to the
other tanks in the system.
There are advantages and disadvantages to be considered when using this
type of system. The water in the central system is common to all tanks
operating on that system. So one of the advantages is perfect control of
the water parameters in all the tanks at the same time. But this is off
set by the fact that should disease enter the system all tanks and fish on
the system are exposed to it. But once again should disease or parasites
become a factor medication can be applied to all the tanks from the same
system at an uniform and controlled rate.
Since the physical layout for each fish room is different almost no two
such systems are the same. I have seen one central system operate as many
as a hundred tanks or as few and three or four. It is amazing what can be
done with the use of PVC pipe and fittings, and the skill required is
within the reach of almost anyone.
Centralized systems can be designed in any number of ways some flow
thorough a single media that the bacteria develop on under water others
use what is known as the drip-dry method which is explained next.
WHAT IS DRIP DRY?
In this system the water to be filtered is dripped on to a very large
surface area such as bio-balls or cinder rocks and the water first passes
though a floss sheet to remove solids then flows as evenly as possible
over the bio-balls or rock in such a way that the surface areas are
constantly kept wet as the water passes by. This is generally done with a
spinning wheel or spray bar of some type. The water then gravity falls
into a return supply tank and is pump feed back to the tanks as filtered
water. It should be kept in mind that for proper growth nitrifying
bacteria require a large and dependable supply of oxygen. There are three
basic bacterial groups that are at work in any filter other than one
strictly designed to remove solids only. These bacteria are,
Heterotrophic, Nitrosomonas and Nitrobacter types. In order to provide the
best growing conditions sometimes-large volumes of air is force blown
through the media as the water trickles by.
In either the submerged type or the drip type system the use of a
constant drip system can be added. In my systems I have arranged it so
that from a low pressure value 25% of my water is constantly being replace
and the old water over flows through a drain to the waste line. I have
found this to be the most effective way to provide the most desirable
conditions to my tanks at all times. Everything is totally automatic in
such a system.
SO WHAT ELSE IS OUT THERE AS
I think the above explains the most common types found in the aquarium
hobby today with the advantages and some of the disadvantages pointed out.
But I must remind you that there are many more of a chemical nature used
in other applications that just might be adaptable to the aquarium. And
now last but not least, there are two other types to consider.
In this type of filter the water is forced by a pump to flow through
fine particles of sand which keeps them in a flowing state at all times.
This system is not new but is new to the aquarium hobby so to speak. It
has only recently been adapted to small-scale use in the home aquarium.
When you can locate and buy one that works well as they are designed to do
this type of filter offers a very large surface area for bacteria to grow
on and therefore has many advantages in a small size with a low cost of
operation. The problem arises in that they tend to clog badly and should
the sand stop flowing as required the bacteria quickly die for a lack of
oxygen and this in turn presents a deadly problem to your fish in quick
order. One other problem I have found with these units is that all I have
tested tend to blow some sand into the tank and this is not a desirable
Now we move on to what I consider to be the ideal filter for the use in a
single tank arrangement, and even should be added to individual tanks on a
THE SPONGE RUBBER FILTER.
I have used these filters for years, in the discus hatchery they offer
more advantages and fewer disadvantages than just about any arrangement I
can think of.
These filters are found now days in just about every pet store or
aquarium shop. They can be seen in all sizes and arrangements from a
single sponge to double or even triple sponge configurations.
The operation of this type of filter is simple and direct. The water is
drawn through the sponge either by air flow or a powered pump. In the most
common packages it is designed to operate much the same way the out side
box filter works, air is released deep in a plastic tube centered in the
sponge that has wholes positioned in such a way that water flows through
these holes and through the sponge and is lifted upward with the flow of
air within the tube. Of course a much greater water turn over rate can
occur if a power head is use to forcefully draw the water though the
One of the great advantages is the simplicity of the entire
arrangement. Another advantage is ease of cleaning and replacement. Then
when you consider that very small fry are protected since they can not be
sucked into the filter under such an arrangement you have almost a perfect
filter. The surface area on a sponge is very large when it is designed
right. I generally keep two or more sponge filters going in each tank so
that they can be removed for cleaning without a lost of filtration.
Cleaning is very easy and simple you just raise the filters in running
water that is near the same temperature as that of the tank. A few
squeezes in warm running water and you can place the sponge back in the
tank ready for operation.
One other advantage I have noticed is that when discus have fry in the
tank and are side feeding them the fry will gather around the dark sponge
filter and peck at any food found there. This is handy when you start
feeding newly hatched baby brine shrimp which are drawn to the sponge
So there you have an over-view of filters. Enjoy their use in the hobby
and don't forget to keep any filter clean. Just because waste is outside
the aquarium does not mean it is out of the system.