Understanding Aquarium
Filtration
Adapted from an article by Steve
Rybicki
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Credits
This presentation was adapted by Tamar Stephens from
an article by Steve Rybicki. The text in this presentation
is taken directly from his article, and is reprinted here
with his kind permission.
The article in its entirety can be found at:
http://www.angelsplus.com/ArticleFiltration.htm
Clip art, photographs, and other home-made graphics
were added for visual interest.
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How much do you know about
aquarium filters?
If you have a big enough filter, it is okay to overfeed your
angelfish?
What are the three kinds of filtration, and which one is best?
Is a filter that creates lots of bubbles good for your
angelfish?
How does mechanical filtration threaten your angelfish?
Can lots of filtration reduce the need for water changes?
Keep reading to find the answers!
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Aquarium filtration is a bit of a
mystery

Aquarium filtration is a bit of a mystery to most people. There is a
common misconception that the filter should take care of
overfeeding and keep the water perfectly suitable for fish.

Manufacturers make a big deal out of it. Most of the new filters
coming to market are large, complex and expensive. The companies
making them lead you to believe that if you are having problems with
your fish, then it's probably due to the lack of filtration.

You may be surprised to learn that the amount of filtration is
the least likely cause of most problems. In this presentation, I
hope to clear up the mystery and make this an easy concept to
understand. Keeping your aquariums clean and suitable for fish is
quite easy as you'll see.
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What are the three kinds of
filtration?
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Getting down to the basics
Let's get down to basics. You can filter water
with three basic methods:
CHEMICAL
MECHANICAL
BIOLOGICAL
Chemical
reaction
removes one
or more
impurities
Traps
particles of
waste
Nitrifying
bacteria break
down ammonia
and nitrites
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Most Filter Systems use a
Combination

Most filter systems involve a combination of at least
two of these and some use all three. We are often led
to believe that all are necessary, yet in my opinion only
one is really important, and effective in most filters.

Now let's take a more detailed look at each and how
much sense it makes to incorporate them into your
filtration methods.
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Chemical Filtration

With chemical filtration
you use an item like
carbon or zeolite to
remove an impurity.

The chemical reaction
that takes place is
usually very short
lived and it's
effectiveness lessens
rapidly from the very
beginning of it's use.
What is activated carbon?
It is carbon that has been treated to
make it very porous, thus increasing
the surface area dramatically.
Activate carbon works by chemically
attracting impurities, which adsorb
(or stick to) the carbon.
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Uses for Chemical Filtration

In my opinion, unless you want to do an extraordinary
amount of maintenance on a continual basis, this type of
filtration is suitable only as a temporary measure.

It's great for emergencies, removing medications from
the water or trying to reduce sudden spikes of toxins.

It's good to have some of these items on hand, but don't
bother to incorporate them into your daily filtration
system. In general, doing so would be a waste of time
and money.
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Mechanical Filtration

This involves the trapping and removal of waste
particles. In concept, this is a great idea. In
reality, most filters cannot do this in a manner
that is effective or convenient for the aquarist.

Most mechanical filters do a great job of
trapping some particulate matter, but
unfortunately they don't get it all. They have a
tendency to move the water too fast, thus
breaking the particulate matter into smaller
pieces. The very small pieces tend to become
suspended.

These suspended micro particles contain the
dangerous heterotrophic bacteria that can
potentially cause great harm to our fish. The
bacteria should be kept away from our fish, but
these suspended particles do the opposite.
They are in the water column and are very
harmful.
Large particles may be
broken into smaller particles
that pass through the filter
and stay suspended in the
water column.
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Heterotrophic bacteria

Heterotrophic bacteria primarily act as
decomposers, feeding on dead plants and
animals, and other organic material such
as uneaten fish food in your aquarium!

Under ideal conditions, heterotrophic
bacteria can double their population in
15 minutes to an hour.

Suppose you overfeed your fish in the
morning, go to work, and come home
about 10 hours later. If the bacterial
population doubles every 15 minutes, the
population will increase by a factor of over
1 trillion!
Example of heterotrophic
bacteria.
Wikimedia Commons
(Public Domain)
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High speed filters are harmful

Filters that move water through the aquarium at higher speeds,
cause this problem to become worse. Small waste particles are the
enemy. Filters that move water too quickly and those that create
a large amount of small bubbles, break these particles into
even smaller pieces and will actually cause this bacteria to
become an even greater problem.

To encourage small waste particles to settle in the filter chamber,
water movement must be the slow enough to cause the particles to
settle. This is very difficult to achieve with most power filters and
canister filters.

Very large aquariums or aquaculture systems will generally have
large filter systems that contain proportionately large settling
chambers, where these fine particles can be eliminated from the
water column.
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Draw from the bottom of the tank

In addition to removing these particles from the
water column, they need to be removed from the
bottom of the tank.

The fins of fish often touch the bottom, and the
waste particles that settle here can cause
problems when the fish rubs against them.

Therefore, a filter needs to draw from the tank
bottom and anything it doesn't get, must be
removed through siphoning.
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Biological filtration

This is the process by which nitrifying bacteria break down
ammonia and nitrites. I will not cover the basics of biological
filtration. That is detailed in many other sources. Just realize that it is
easy to have adequate nitrifying bacteria in aquariums containing
ornamental fish.

In intensive aquaculture, it is common to raise as much as 1 lb of
fish per gallon of water, with relatively small biological filters. That
would be equivalent to raising somewhere around 100-150 adult
angelfish in a 20 gallon tank.

In such a system containing angelfish or other ornamentals,
problems from dissolved organics and heterotrophic bacteria
would destroy the fins or kill the fish long before ammonia or
nitrites became a problem.
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A small biological filter

A surprisingly small biological filter can handle
the ammonia produced in the average aquarium
containing ornamental species.

So, although biological filtration is very
important, it's also very easy to provide with a
small inexpensive filter.

The only requirement is that the filter does not
clog so the nitrifying bacteria has constant
exposure to oxygenated water.
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Tying it all together

As you have probably surmised by this point, chemical
filtration is not practical or effective for most aquarists.

In addition, mechanical filtration is normally performed in
a manner that can actually be detrimental.

Unfortunately, most aquarists rely heavily on these and
are not aware of the best way to utilize them. In fact,
some of the most expensive filters can also be some
of the least effective.
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Filtration Goal

Your goal should be to get a filter that moves water
slowly through a settling chamber, removes waste from
the bottom, and one that is easy to keep from clogging.

To accomplish this in an inexpensive manner on
aquariums that are not part of a recirculating system, my
recommendations for filtration are as follows.

In aquariums that have a substrate, I recommend an
undergravel filter. They are extremely effective and
easy to maintain when setup properly. Their large
surface area helps to reduce overall water speed and the
area under the plates makes for a very effective settling
chamber.
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Setting up an undergravel filter

When setting one up, place the
filter plates on the bare tank
bottom.

Then cover them with a layer of
polyester batting. The batting will
prevent the substrate from falling
into the filter plates and it will also
provide greater surface area for
nitrifying bacteria. The quilt batting
found in sewing stores works well.

Cover with a substrate that is fine
enough that no food particles can
fall beneath the surface of the
substrate. This will allow the easy
siphoning of uneaten food that
cannot be trapped.
Photo from:
http://www.drsfostersmith.com
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Clean the Gravel

When doing a water change, use a
gravel cleaner to remove particulate
matter. Do this to no more than one
half of the substrate during any one
water change. Vary the location of
the substrate cleaning with each
water change.

Using this technique, I've
maintained beautiful, healthy
aquariums for more than 20 years
without ever having to add any
addition filters or perform any other
maintenance.
Photo from:
http://www.drsfostersmith.com
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Sponge filters

For breeding operations or the raising of fry, bare bottom tanks should
be used. In these situations, nothing beats a simple sponge filter for
effectiveness and ease of maintenance.

However, not all sponge filters are equally good. You must choose one
with a pore size appropriate for the fish size being kept.

The object is to keep the pores from getting clogged with food or fish
feces. It should provide adequate surface area for nitrifying bacteria.

The sponge type should allow easy rinsing of the filter. Yet, it must
also allow space for the settling of organic debris.
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Bare-bottom Tank with Sponge
Filter
Juvenile angels
in a bare-bottom
tank with sponge
filter.
Photo from: http://www.angelsplus.com
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More on Sponge Filters

If one sponge filter isn't enough, use more.

Slow to moderate flow rates are essential. The smaller the filter, the
slower the flow rate must be. The inside of the sponge becomes the
settling chamber. Too much flow, and the settling chamber will not
work.

It is important that the sponge filter lifts water from the bottom
of the tank. It not only makes it easier to get particles off the bottom
and into the filter, but it turns the water over in the tank more
efficiently for greater gas exchange. Therefore, the sponge filter
should sit flat on the bottom.

Those that are on a pedestal, may create dead spots in the
aquarium, and are the worst at trapping particles that make it to the
tank bottom.
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A Note about Filter Size

Filters are not sized for a particular number of gallons of water.

They work by consuming ammonia and nitrites produced by a
particular bio-load. The bio load consists of the total mass of fish and
heterotrophic bacteria in the tank.

It matters not if the tank is large or small, filters have to be sized
accordingly to the number and size of fish in relation to age, water
temperature, pH and a few other factors. It is something you can only
figure out for a given situation through experience.

As long as the water isn't moving too fast in the tank, it doesn't hurt
anything to over-filter, except possibly your wallet.
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Water Changes!

So far, providing the needed filtration sounds fairly simple, but don't
get too excited. One of the more important aspects of filtration can't
be performed perfectly by any filter and is usually done manually.

That is, the aquarist must periodically remove mulm with water
changes, and they must also occasionally rinse the filters to keep
them from clogging. Water changes are what is used to remove
harmful dissolved organics and nitrates. Most aquarists worry about
ammonia and nitrites. However, they are easily controlled and
seldom a problem for anyone other than a beginner with poor
husbandry practices.

Dissolved organics and heterotrophic bacteria are the real
concerns, yet they are almost impossible for an aquarist to
detect. It is critically important to keep them at low levels. Water
changes are the most effective way to do this.
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Cleaning Sponge Filters

A note on how to rinse sponge filters: Gently
squeeze the sponge into fish-safe water (we use
water taken out of the aquarium from a water
change).

Do not rinse it too thoroughly. You don't want to wash
all the nitrifying bacteria out of it.

Never clean them in a washing machine or
dishwasher. This will essentially kill all the good
nitrifying bacteria and render your filter useless.
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You can never do too many water
changes!

Water changes can even be used to remove uneaten
food, but hopefully your fish husbandry is good enough
that uneaten food doesn't exist.

The frequency needed for water changes will vary
greatly with fish density, temperature, amount of food
being put into the tank, pH and a few other factors.

It's better to err on the side of more water changes. You
can perform too few, but never too many.
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Final Remarks

It should be a relief to know that through the combination
of properly designed sponge filters, correct feeding, and
adequate water changes, you can filter an aquarium
better and at lower cost than any other practical method.

Don't fall prey to the hype surrounding expensive
aquarium filters. There exists some very effective,
sophisticated and expensive central filtration systems
designed for hatcheries, however for practical filtration
on individual aquariums, nothing works better than the
simple filters recommended here.
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Enjoy your fish!
Steve Rybicki
The End
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