Choose the Right Filter For Your Tank
The filtration system is the single most important factor
in maintaining a healthy environment and healthy fish.
A recent article in Aquarium
Fish Magazine estimates that more than 80 percent of all fish
health problems in aquariums are directly linked to improper or
There are several types of filters used by today's hobbyists.
An undergravel filter is the very least a tank needs to
THE UNDERGRAVEL FILTER:
An undergravel filter is a slotted plate situated inside the aquarium on
the bottom glass under the aquarium gravel. Air bubbles or power heads are
used to pull water down through the gravel and up through the lift tubes.
During this process, large particles are trapped in the gravel
so that they are not suspended in the water - mechanical filtration.
Additionally, nitrifying bacteria live on the surfaces of the
individual gravel grains and "processes" the water as it goes by,
converting ammonia to nitrite and nitrite to nitrate - biological
An undergravel filter plate should cover the entire bottom of the tank,
and the gravel bed should be 2 to 3 inches thick. Gravel should have an
average diameter of 3 millimeters (1/8 inch) to ensure lots of surface area
for bacteria to grow on while providing enough space among the pieces to
permit good water flow with minimal clogging.
Water flow through the filter should be between 0.5 and
1.5 gallons per minute for each square foot of aquarium bottom area.
Should the undergravel filter bed become partially clogged with
particulates, the water will channel around those areas and reduce
nitrifying (biological cleansing) activity -
the process of converting ammonia to nitrite to nitrate.
The result will be rising concentrations of ammonia.
Meanwhile, without oxygenated water passing through some
areas of the gravel, anaerobic regions (areas with minimal amounts of oxygen) will develop and become inhabited by undesirable bacteria (e.g., heterotrophic bacteria that produce deadly hydrogen sulfide gas, which smells like rotten eggs). If the gravel bed
becomes totally clogged, the nitrifying bacteria (beneficial bacteria)
will die and heterotrophic bacteria (undesireable bacteria)
will take their place.
There are two ways to deal with this problem. One is to use a
hydro-cleaning device, sometimes known as a gravel "vacuum."
When siphoning water from the tank, the gravel is churned about in the
large end of the siphon hose and the particulate matter is removed
while the gravel remains in the tank.
The other method is to use efficient mechanical filtration to remove
most of the solid material before it settles into the undergravel filter.
Some people add a tank-mounted filter (below) as a supplemental mechanical
filter to pull particulates from the water rather than have all of
them drop to the bottom of the tank and begin to clog the gravel.
An undergravel filter is the least expensive and most common of all filters.
It requires a filter plate and a pump or power-heads. Power heads usually
give the undergravel filter a boost in that they move the water through
the filter with the most speed and agitation.
TANK-MOUNT POWER FILTERS:
Tank mounted filters usually hang on the outside of the tank.
They pull water out of the tank and let it trickle back into the tank.
During the process, the water is passsed through at least one and usually
two filter pad inserts. The first traps any large debris that may be
floating in the tank. The other allows nitrifying bacteria
to grow on its surface so that biological filtration
can also occur as the water trickles through.
The water pours back into the tank, dropping through a small amount of air
space like a mini waterfall, which agitates the surface of the water
and enhances the oxygenation of the tank.
It is very important to keep the mechanical filter pad clean.
If it gets clogged, the water will bypass that pad and hit the biological
filter pad full of particulates which will also soon clog the second insert.
However, it is equally important that you not continually distrub the second
or biological pad. Too festidious a cleaning or using chlorinated water
to wash the second pad can destroy the beneficial bacteria which
are cleaning the tank.
Tank-mounted filters are a very good supplemental filter. They are not
as expensive as most canister or wet/dry filters (below). Adding
a tank-mounted filter to you existing tank will enhance the water quality because
it will provide more filtration. More and better filtration will
allow you to keep more fish in the same tank.
Another type of filter is the wet/dry filter.
THE CANISTER FILTER:
Canister Filters are one of the most popular and best types of filters. They provide all three types of filtration: mechanical, chemical, and biological filtration for larger tanks or tanks with lots of fish, but they take up less room than wet/dry filters (below). Some are so good at particulate filtering that they can actually be called a water polishing filters.
Depending on the model, they will contain one, two, or three media baskets. The idea is to push the water through the baskets, pulling pollutants out of the water as it passes through the media held in the basket. Canister filters take a little more work to set up (although they are getting more sophisticated every day), but their capacity and filtering ability are much better than power filters. Media needs to be changed or cleaned. Most have convenient snap-closures and some have quick disconnect hoses to make maintenance of the filter easy. Some are self-priming to make re-starting a breeze. They can be used for freshwater, saltwater, and cichlid tanks.
THE WET/DRY FILTER:
Wet Dry filters (also known as trickle filters) work on the same principle
as undergravel filters, but implement the concept differently.
The trickle filter's biological filtering bed is outside of the tank.
Aquarium water enters at the top of the filter column and trickles
downward through the medium (e.g., stone, specially designed plastic
media, fiber materials, etc.), which is not submerged, thereby collecting oxygen in the process.
The nitrifying bacteria inhabit the surface of the medium and
process (clean) the water as it trickles by. The water then collects at
the bottom of the filter column and is pumped back to the tank.
This design provides for efficient nitrification, as well as good
aeration (oxygenation) of the water. Some of the better commercial trickle
filter designs incorporate drawers for mechanical filtering media and
GAC (high quality granular activated carbon)
so that the entire filtration system is built into one unit.
Trickle filters are particularly well suited for marine aquariums,
where dissolved oxygen levels are low, and for freshwater aquariums that
use a soil substrate for plantings, making undergravel filtration impossible. Unlike the undergravel filter, clogging is not a problem with trickle filters.
For best operation, the volume of the trickle column should equal
about 8 to 10 percent of the tank volume. The water flow rate should be
4 to 5 times the tank volume per hour.
For the most efficient nitrification, the filter surface area should be
designed to yield 0.5 to 1.5 gallons per minute per square foot.
Both undergravel and trickle filters are sensitive to power failures.
If the filter ceases to operate for more than 24 hours, halting the
flow of water through the biological medium, the nitrifying bacteria will
begin to die. Once water flow begins again, conditions will be
similar to starting a biological filter in a new setup. In fact,
conditions could be worse than a new system, as the dead and putrifying
bacteria could poison the tank with a fast load of ammonia upon
the re-start of the tank.
THE BEST FILTRATION:
If only mechanical filtration is used, large particulates may be
trapped in the mechanical filter medium, but
there will be minimal biological filtration from the nitrifying
bacteria in the mechanical filtering medium.
Dissolved organic carbon such as
fish waste and plant degredation will not be removed from the water and
toxins can build up.
This limited amount of biological filtration will be very sensitive
to changes in fish load (i.e.,adding more fish or fish growth),
changes in feeding rates, and even variations in water temperature.
Nitrifying bacteria will have no surface to which to cling except
in the mechanical filter medium.
Moreover, scrupulous cleaning of the mechanical medium will wash away
most of the nitrifying bacteria, leading to high ammonia levels in the water.
Adding a layer of Activated Carvon for chemical filtration of
organic waste will not change the fact that there is no effective and
reliable method for removing nitrogenous wastes. Carbon is used to remove
impurities such as chlorine, not ammonia or its by products.
In a setup with only an undergravel filter, there is practically no chemical
filtration for dissolved organ compounds.
In addition, without an efficient mechanical filter,
the nitrification bed will eventually clog with particulates.
Nitrification will be reduced and life in the tank will decline.
In contrast, a filtering system comprised of all three components
(mechanical, chemical and biological) provides all requirements for
maintaining a healthy aquarium.
A typical wet dry filter does all three of these things.
If cost is a consideration, an efficient
setup consists of one outside power filter - either a hang-on-the-back
unit or a canister - with separate compartments for mechanical media,
GAC and ion exchange resin. It's important that the filter is large
enough to accommodate the appropriate amount of filtering material.
An alternative setup uses two independent filter units.
An outside power filter that contains mechanical media and activated carbon
to remove particulates and dissolved organic compounds
is run in conjunction with an undergravel filter.
Although a complete filtration system will cost a little more in the beginning,
you save in the long run by avoiding
the costs of replacement fish for those that died and medications for
fish that become ill. More importantly, your fish will thrive and your
aquarium will be more enjoyable. A properly filtered aquarium requires
less maintenance than one with incomplete or inadequate filtration.
No filtration system, however, can keep aquarium water as clean and
healthful as it was from the tap. Over time the
water quality deteriorates. Therefore, periodic water changes of 20
percent of the aquarium water are a necessary part of your total filtration
system. A conscientious hobbyist can achieve the necessary good water
quality with a minimal amount of effort and a good filtering design.