There are more than one way to filter your aquarium, which makes your choices a bit more difficult. There are a few things that you will have to consider when choosing which method to use. Are you going to have live plants? Are you going to use the tank to breed? And so on and so on. I will try and clear this up for you here, so as to make your choice easier.
Contents
A brief
description on the different types. (It's copywritten so this is a link
to it.)
Why you need filtration and how it works
Nitrogen cycle chart
Water changes
Biological filtration
Mechanical filtration
Chemical filtration
Filter types
Corner
Undergravel
Sponge
Power filter
Canister and Submersible
Wet/Dry (Trickle)
Protein skimmers
Fluidized bed
Denitrators
Algal Scrubbers
Chillers
Sterilization
Sometimes we forget that fish kept in an aquarium are confined to a
very small quantity of water as compared to their natural habitats in the
wild. In the wild, fish wastes are instantly diluted. But in an aquarium,
waste products can quickly build up to toxic levels.
These waste products include ammonia released from your fishes' gills,
fish poop, and scraps of uneaten food. The food and the poop will also eventually
decay, releasing ammonia. Even small amounts of ammonia will kill your
fish.
Obviously, the more sources of fish waste, the quicker and greater
the ammonia problem. A small heavily-fed tank with lots of large fish will
have much more ammonia than a large tank with one seldom-fed small fish.
But for both these cases you need some form of aquarium filtration to control
the toxic ammonia.
Some aquarists try to control ammonia levels exclusively by changing
the water. This is helpful, but impractical because of the frequency and
size of the water changes required.
Fortunately, there is an easier way! In fact, the world is full of
bacteria that want nothing more than to consume the ammonia and convert it
into less toxic substances. For many an aquarist, this process occurs without
their knowledge or help. However, the smart aquarist will learn how to take
advantage of this beneficial bacteria by maximizing its growth.
When you start a new fish tank, colonies of beneficial bacteria have
not yet had the chance to grow. For a period of several weeks this is hazardous
to fish. You must gradually build up the source of ammonia (i.e., start with
only one or two small fish) to allow time for the beneficial bacteria to
grow. This is called "cycling" your tank.
Remember that the bacteria break down the ammonia into substances (first
nitrite, then eventually nitrate) that are merely less toxic, rather than
non-toxic. Many fish can tolerate reasonably high levels of nitrates, but
over time the nitrates will accumulate until they, too, become toxic. Also,
because nitrate is a fertilizer, high nitrate levels can lead to excess algae
growth.
Water changes
Although there are many ways to remove excess nitrate, the most effective
way is to regularly change part of the water. This is one of the most
neglected and important parts of aquarium maintenance! How often and
how much you need to change depends a lot on the waste load in your tank,
and the sensitivity of your fish. You don't want to change ALL of
the water at any point in time because the change in water chemistry will
be stressful to your fish. The best way to decide how often and how much
to change your water is to monitor your water quality with water tests. As
a minimum, if your tank is new, you should test for ammonia and perhaps nitrite.
In established tanks you should monitor for nitrate accumulation. Water tests
are the most reliable way to know how well your aquarium filtration works.
For an average tank, you should change no more than one third of the
water in 24 hours. Many aquarists with average aquariums change a quarter
of the water every two weeks. Your aquarium is probably not average, and
you really should measure nitrate levels to determine your water change
schedule.
Biological filtration
Biological filtration is the term for fostering ammonia-neutralizing
bacteria growth. It is so important to the health of your aquarium that we
should look at how this process works more loosely. (There are other types
of wastes that can cause problems, but the regular partial water changes
needed to control nitrates are typically enough to control other forms of
waste as well.) Mother Nature provides several types of bacteria that
break down ammonia into progressively less toxic compounds. First,
nitrosomonas breaks ammonia into nitrites. Then
nitrobacter breaks the nitrite into nitrate. These bacteria are not
harmful and are quite abundant in nature. They are so common that we do not
need to add them to our aquariums; nature does it for us.
In the presence of ammonia and oxygen these bacteria will naturally
multiply. The bacteria attach to the tank, rocks, gravel, and even tank
decorations. Note that we have not yet said anything about a physical filter.
This is because biofiltration bacteria require only
1. A surface upon which to attach,
2. ammonia for food, and
3. oxygen-rich water.
This sounds so simple; why do we need a physical filter? Actually,
if you limit the amount of fish to what the natural biofiltration can handle,
you do not need a physical filter. Unfortunately, you cannot support very
many fish with only the natural biofiltration.
In the last few decades, the hobby has seen many new types of biological
filters invented which can vastly increase the capacity of the bacteria colony
to provide biological filtration to your aquarium. In essence, all of these
types of filters provide additional surface area for bacteria attachment
and increase the available oxygen dissolved in the
water.
Mechanical filtration
Remember that ammonia comes directly from the gills of your fish, but
also from decaying fish poop and food scraps. If you can mechanically filter
out the poop and the waste food before it gets a chance to decay, you can
be a step ahead in the game. Not to mention that these wastes are ugly and
can detract from the beauty and enjoyment of your aquarium.
Simply stated, mechanical filtration is the straining of solid particles
from the aquarium water. Mechanical filtration does not directly remove dissolved
ammonia. Most common mechanical filter media do not remove microscopic bacteria
and algae from the water. Neither will mechanical filtration remove any solids
trapped by gravel, plants, or decorations.
You will need another method to remove the solid wastes from the nooks
and crannies of your aquarium. One of the easiest methods is to "vacuum"
the gravel, etc., as part of your regular water change routine and everybody
should do this. (Note that those marine aquariums which use ``live substrates''
are an exception.) Some people install circulation pumps, known as wave makers,
to improve the chance of catching solid wastes in the mechanical filter.
The four most popular mechanical filtration media are sponges,
paper cartridges, loose and bonded floss media which are reusable to
different degrees. Clean paper cartridges have the smallest openings and
clean bonded floss has the largest openings. Clean sponges and clean loose
floss fall somewhere between.
A filter media with small openings catches finer particles, but clogs
faster. Also, as a rule, a physically large filter area will clog more slowly
than a small filter. As the filter media gets dirty it will trap smaller
and smaller particles. At some point the media is so clogged that it will
not pass water.
SUMMARY: A good mechanical filter is one that traps enough solids to
keep the water clear without plugging too
often.
Chemical Filtration
Chemical filtration, in short, is the removal of dissolved wastes
from aquarium water. Dissolved wastes exist in the water at a molecular
level, and fall into two general categories, polar and
nonpolar. The most common chemical filtration method involves filtering
the water through gas activated carbon which works best on the nonpolar wastes
(but also removes polar wastes). Another effective method is protein
skimming, which removes polar wastes such as dissolved organics.
Granular activated carbon (GAC) is manufactured from carbon, typically coal,
heated in the presence of steam at very high heat. This process causes the
carbon to develop huge numbers of tiny pores, which trap nonpolar wastes
at the molecular levels by means of absorption and ion exchange, and removes
heavy metals and organic molecules, which are the source of undesirable colors
and odors, through a process known as molecular sieving.
The best GAC for filtering water is made from coal and is macroporous
(having larger pores). A good macroporous activated carbon feels light (not
dense) and fizzes and floats when initially wetted. GAC intended for removing
wastes from air (such as odors) are commonly made from coconut shell and
are microporous. Carbons for filtering air feel more dense.
Some people (especially those with reef aquaria) are concerned about
phosphate leaching from activated carbons. As a rule, buy only carbons made
by reputable aquarium supply companies which have been acid washed during
manufacture to minimize ash content. Carbons low in ash also help reduce
the chance of undesirable pH shifts. Low ash carbons typically have lower
phosphate leaching levels too.
The phosphate in GAC stems from the fact that activated carbon is
manufactured from coal, which was once living plant matter. All living matter
is high in phosphates. The leaching of phosphate from GAC is known to be
high initially and to decrease over time. This problem can be mitigated
significantly by presoaking your activated carbon for a few weeks before
use.
Some people are concerned about GAC removing trace elements required
by plants and invertebrates for healthy growth. Trace element depletion is
a problem in planted aquaria and minireefs, with or without activated carbon.
The potential benefits of activated carbon are great enough that on whole
you will be better off using it. If trace element depletion is a worry, use
a trace element supplement in conjunction with the activated carbon.
GAC cannot be rejuvenated outside a laboratory, but fortunately, it
is cheap enough to use liberally. Always wash your carbon before use to remove
the dust that accumulates during shipment. Advice on how much to use vary,
but smaller amounts changed more frequently seem to work best. You probably
want to experiment, but 1/2 cup per 20 gallons water, changed monthly is
a good starting point. In summary, activated carbon is an excellent, cheap
and effective filtration method which is highly recommended for all
aquaria.
A variety of special chemical filtration media have been developed
to remove specific chemicals. A common one is made from the zeolite clay
(also used as some cat litters), and is marketed under such brand names as
"Ammo-Carb". This media removes ammonia from water, and is good for short
term use. The aquarist should be aware that if zeolite is used, especially
when cycling a new aquarium, then the establishment of natural biological
filtration will be delayed or disrupted.
Protein skimmers are primarily used in saltwater aquaria, especially
reefs. They have the remarkable ability to remove dissolved organic wastes
before they decompose. The process involves taking advantage of the polar
nature of the organic molecules, which are attracted to the surface of air
bubbles injected into a column of water. The resultant foam is skimmed off
and
discarded.
FILTER TYPES
Corner filters
For decades, hobbyists have successfully kept fish healthy and
happy through the use of the $2.49 corner filter. Typically, they are
clear plastic boxes, which sit inside the tank. An air stone bubbles air
through an air lift tube, which forces water through a bed of filter floss
or other media. mechanically filtering the water. Colonies of bacteria build
up on the media, providing excellent biological filtration. (It is important
to change only some of the media at any given time! This way the bacteria
does not get wiped out.) Nowadays people don't use corner filters as much
because they're ugly, take up space in the tank, and require a bit more frequent
maintenance than other filters. But you can't beat the price.
Another use of the corner filter, that is not really matched by other
filter types, is as an impromptu quarantine tank filter. If you have the
need to set up a second tank on the quick, you can take some gravel from
an established tank and put it in a corner filter, and immediately, you will
have a functioning biological filter. This way you can turn a five gallon
bucket into a quick and cheap hospital/quarantine tank on a moment's
notice.
Undergravel Filters
Fish stores commonly sell undergravel filters (UGF's) to beginners
in "aquarium kits" because they are cheap, and they work (for a
while). UGF's work by slowly passing water through the bottom gravel, which
sits on top of a perforated plate. The water can be pumped with an air lift,
with bubbles air lifting the water in a vertical tube attached to the filter
plate. Also, some people prefer the increased water flow achieved with
submersible pumps, called powerheads, attached to the same lift tubes.
UGF's make good biological filters, because the slow flow of water
through the gravel fosters large colonies of beneficial bacteria which neutralize
toxic ammonia. The hitch is, that UGF's are awful mechanical filters. Fish
waste gets pulled out of sight into the gravel. Before you know it, the gravel
clogs up. You then have a big mess and a health risk to your fish!
A partial solution to this dilemma is to run the powerhead in reverse,
sending water up through the gravel. This technique is known as
Reverse-flow Undergravel Filtration (RUGF); conversion kits or special
powerheads can be purchased to accomplish this. The intake of the powerhead
is covered with a porous sponge which serves to "prefilter" out some of the
waste that can clog the gravel. In actually practice, this helps, but is
only a partial solution.
If you choose to use an UGF/RUGF, you must regularly vacuum your
gravel. Fish stores sell siphon hoses with a "wide mouth gravel vacuum
tube" attachment that "washes" the gravel during your regular water changes.
IF you clean your gravel regularly, and maintain a regular and frequent
partial water routine, UGF's and RUGF's are an economical and effective aquarium
filter in freshwater aquariums, and in lightly stocked saltwater fish-only
aquariums.
Sponge filters
Sponge filters provide an efficient and cheap form of
biological filtration. Water is forced through a porous foam, either
by a powerhead, or air bubbling through an airlift tube. Water flowing though
the sponge allows the growth of a colony of beneficial bacteria which neutralizes
toxic ammonia.
One style of sponge filter uses two sponges attached to one lift tube.
These have the advantage that the sponges can be cleaned one at a time, reducing
bacterial loss. Also, one of the sponges can be removed and transferred to
a new tank, bringing with it a colony of beneficial bacteria, and thereby
"jump starting" the cycling of a new tank. Some enlightened fish stores sell
these double sponge filters to beginner customers when they sell a tank kit.
They take one of the new sponges out of the "box" and swap it for a old
established sponge in one of their tanks in their store which is carried
home in a plastic
bag.
Power filters
Most people agree that power filters are much easier to maintain and
can be as economical as undergravel filters. There are many styles of power
filters, but the most common hangs on the back of the tank. A siphon tube
pulls water from the tank into the filter box and passes the water though
a mechanical filter (typically a porous foam sponge). The sponge doubles
as a biological filter. A internal pump then returns the filtered water into
the aquarium. These power filters come in many sizes suited for small to
large aquariums.
The foam sponge can be easily inspected for clogging or removed for
cleaning. You must clean the sponge regularly to remove the solid wastes
before they decompose and dissolve back into the water. It is quite important
that when you clean the porous foam that you do not kill the bacteria colony
through the use of detergents, very hot or very cold water. A safe and easy
way is to rinse the foam sponge in the bucket into which you have just drained
some tank water during your regular water change routine.
Power filters now come with all sorts of fancy "features". Most allow
placement of a chemical filtering media, typically granular activated carbon,
in the water path.
Another development in the last few years is the "wet-dry wheel "(called
a _biowheel_ by one manufacturer). The beneficial bacterial colonies that
neutralize toxic ammonia require an oxygen rich environment to grow. The
"wet-dry wheel" passes water over a water wheel device which sits outside
(on the edge) of the aquarium. This rotating wheel maximizes available oxygen
allowing a large bacteria colony to flourish. One drawback is that these
wheels have been known to jam, so you need to check them frequently. Other
than this minor point, the "wet-dry" wheel is an excellent method of providing
vigorous biological
filtration.
The Canister Filter
Canister filters have some similarities with the "hang on tank" style
of power filters, but the essential difference is that canister filters are
designed to provide more powerful mechanical filtration. Typically, the water
is pumped, at moderate pressure through a filter material, such as glass
wool, or a micron filter cartridge. Canister filters are especially useful
in aquaria with large or numerous messy eaters that generate a lot of waste.
For these filters to be effective they must be frequently cleaned, to avoid
the decomposition of waste in the water stream.
These filters usually sit on the floor below the tank, but also can
hang on the tank, and in some designs even sit inside the tank, in which
case they are called a ``submersible filter''. Some hobbyists attach a "wet-dry
wheel" to the outflow of their canister to improve the biological filtration
capacity of this type of filtration
system.
Wet/Dry Filters
Also known as trickle filters, wet/dry filters work on the principle
that the beneficial colonies of ammonia neutralizing bacteria grow best in
the presence of well oxygenated water. By "trickling" water over unsubmerged
plastic gizmos or other media, wet/dry filters provide a very large air/water
surface area. They come in many shapes and sizes. The boom in successful
saltwater aquariums in the 1980's can be attributed to the use of this filter
type.
Many things can used for the media, with the best providing great amounts
of surface area, while at the same time having large openings to reduce the
tendency to clog and ensure efficient gas exchange. The problem of clogging
of the media can also be reduced by prefiltering the water with an efficient
mechanical filter, and (when used) with a protein
skimmer.
Protein skimmers
(aka Foam Fractionators)
Protein skimmers were initially developed for use in industrial sewage
treatment plants where they are also known by the term foam
fractionator. Protein skimmers have the unique ability to remove
dissolved organic wastes BEFORE they decompose! This is a neat
trick which is accomplished by taking advantage of the fact that organic
chemicals are attracted to the surfaces of bubbles which are passed in large
numbers through a column of water. The foam is then "skimmed" off the water,
while at the same time removing the organic wastes. The foaming process only
works in a water with high pH and salinity, and as a result skimmers are
primarily for saltwater use.
The protein skimmer is largely responsible for the boom in reef aquaria
in the 1990's, due to the high water quality possible with this type of
filtration. A current "state of the art" in reef systems is based upon the
use of protein skimmers and live rock without the use of a wet/dry filter.
This school of thought is known as the "Berlin
method".
Fluidized bed filters
Very recently, some hobbyists have reported success with a new type of filter which uses a fluidized bed of sand. This filter is roughly similar in principle to the reverse flow undergravel filter, but with much higher water flow. The higher water flow keeps the sand clean of debris, while at the same time allowing the development of large and efficient colonies of beneficial bacteria. Reported problems include oxygen depletion and clogging.
Another specialized type of filter is designed to help in the control
of the accumulation of nitrates, the end product of the neutralization of
ammonia by the biological activity of bacteria. These fall into two categories,
the anoxic bacterial, and the plant/algal scrubbers (discussed in the next
section). It has been discovered that colonies of bacteria which grow in
oxygen poor environments can be harnessed to biologically consume nitrate,
and release harmless nitrogen gas. This method is achieved in one of two
ways. The process was first developed in the 1980's through the use of a
box system, coil, or porous foam block which allowed very slow transmission
of nitrate-laden water. Inside the box/coil/foam, sugar was placed, and the
slow passage of water quickly became anoxic. In these anoxic conditions,
bacteria would grow and consume excess nitrate. Many aquarists have reported
failure in their attempts at this type of filtration.
More recently, hobbyists have developed similar anoxic conditions below
plates at the bottom of their tanks buried in fine sand. In the saltwater
systems, these sand beds are referred to as "live sand". In freshwater planted
systems, fine grain substrates are allowed to develop anoxic zones which
probably also have a denitrification capability.
The Berlin Method of reef aquariums involves the use of large quantities
of live rock harvested from tropical reefs. Aquarists report good nitrate
control in live rock systems, which, though not well understood, probably
involves the denitrification of the nitrates within the interior of the rocks.
Another school of thought is that the heavy growths of calcareous algae on
the live rocks in Berlin Method reef aquariums consume
nitrate.
Algal Scrubbers
Algal scrubbers use live algae to do the "filtration". Water is run over a wire mesh in a trough under bright lights, where algae is encouraged to grow. The growth of the algae removes some pollutants from the water. This is a controversial form of filtration for reefs and large marine ecosystems invented by Dr. Adey at the Smithsonian. Some believe it is a complete filtration solution, others claim its use leads to poor water quality and algae growth in the tank as well. In freshwater planted aquariums vigorous plant growth has been observed to beneficially consume excess dissolved nitrates.
While not really a filtration, saltwater aquarists occasionally have
the need to lower the temperature of their aquarium water. The high light
levels needed in reef aquaria involve a build up of excess heat. Use of a
hood fan and removal of the ballast from the vicinity of the tank can also
help. Submerged pumps are also a source of unwanted heat, and as a solution,
reef aquarists favor the "non-submerged" pumps due to the decreased transfer
of heat to the water.
A little recognized source of heat control is through the natural cooling
effect of evaporation in wet dry filters, and through the flow of air over
the surface of the aquarium. Nevertheless, additional cooling is often required,
especially in warm climates. This is achieved through the use of "freon"
style cooler units similar to home refrigerators. They either pass the water
through a heat exchange unit, or pass coolant through a heat exchanger in
the tank. Those chillers are expensive but not many people have had success
in the "do it yourself" construction of chillers. (The "dorm" type of
refrigerator is not powerful enough to be of use, just in case you were thinking
about
this.)
In especially sensitive aquaria, infections resulting from water born
parasites, fungi, bacterium and vires can cause serious problems. Water
sterilization is most beneficial for breeders (as it can help control infections
of incubating eggs), for centralized multi-tank filtration (to control the
spread of disease between tanks), and for delicate and/or costly setups such
as large tanks and reef systems (as a safety measure). It is important to
remember that a healthy aquarium depends on beneficial bacteria typically
growing on media in your filter which neutralize ammonia. At most, your
sterilizer can kill some water born pathogens, but total sterilization is
not possible or desirable. Aquarists who practice prudent quarantine procedures
for newly acquired fish generally do not need to sterilize.
Two main types of sterilization are used, ozone injection and ultraviolet
irradiation.
Ozone
Ozone gas is highly reactive and is a powerful oxidizer of organic
pollutants, including living pathogens. Another benefit of water treatment
with ozone gas is that it systematically reduces dissolved organic compounds
in the water stream which increases the reserve capacity of the water to
oxidize organic waste throughout the aquarium. Ozone laden water also improves
the ability of protein skimmers to generate foam which increases their overall
performance.
Prior to the discovery of the live rock/protein skimmer "Berlin Method"
style of reef keeping, ozone injection was considered part of a "state of
the art" filtration system, especially among Europeans in the 1980's. The
trend of late is towards the more simple and natural Berlin Method. Though
ozone use remains beneficial, it is being used less in recent years among
reef keepers. Ozone gas is produced by devices which create a spark
in dry air. As humidity drastically reduces the efficiency of ozone generators
most aquarist choose to pretreat the air for the ozonizer with a dehumidifier.
Ozone gas is highly corrosive, all elements (especially rubber) which can
come in contact with ozone must be made from ozone safe materials (commonly
silicone). Residual ozone can be efficiently stripped from air by passing
the air through activated carbon. Ozone must not be allowed to enter your
aquarium because it can kill your fish and invertebrates and/or damage the
beneficial bacterial in your biological filter. Also, ozone gas is unsafe
to breath and can cause irritation even in small concentrations.
Ultraviolet Sterilizers
High intensity ultraviolet light destroys the DNA in living cells and
can be an effective means to control living pathogens. The most effective
UV light is the high energy UV(C) light roughly at the wavelength of 250
Angstroms. To be effective, UV Sterilization (UVS) must expose the pathogens
to high enough light intensity for a long enough period of time. Martin Moe
cites 35,000 to 100,000 microwatts per second per square centimeter as the
norm, which works out to roughly 10 to 25 gallons per hour per watt (or less
for units not operating at peak efficiency). Common problems which
can reduce efficiency and kill rate are:
1. Allowing the water to flow too fast past the UV light.
2. Light blockage due to a build up of salt deposits or bacterial slime on
the bulb.
3. Fading of the light due to age of the bulb (which typically have a six
month life.)
The same property of this light that kills germs can damage your eyes,
and special care MUST BE TAKEN to avoid direct or indirect eye
contact with this light. [This is especially serious because the damage occurs
inside your eyes before you feel any pain. Too many people have already damaged
their eyes in this way!] The UV(C) light does not penetrate water very well,
so to be effective, UV Sterilizers commonly position the UV bulb close to
the water which also can pose a risk of electrical shock should the bulb
break, etc..
There are three types of UV Sterilizers:
1. Tray type. (Typically homemade) with UV bulbs suspended in a reflecting
fixture over a shallow tray of slow flowing water. Benefits: easily cleaned,
can be cheap, can be made large enough for commercial applications. Problems:
safety risks to your eyes, too large and awkward for many home uses.
2. Tube type, wet bulb. Tube types have the benefit of exposing all sides
of the UV tube to water with no reflector. The water passes directly past
the bulb which is mounted in a waterproof tube. Benefits: cheap, compact
and effective. Problems: difficult to clean the slime accumulations from
the bulb, safety risks due to electrical shock.
3. Tube type, dry bulb. Similar to above, but the UV tube is surrounded by
a quartz tube [glass blocks UV(C) light] insulating it from the water. These
are more expensive and probably safer. Changing the light bulb is easier
and dry bulb tube types can have a internal device to wipe slime from the
quartz tube. Some of these types come with sensors to monitor the intensity
of the light to let you know when to replace/clean the bulb.
etc..
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