Aeration and Filtration
Although aeration can be achieved completely
independently of filtration, the topics have been combined
here because many filters provide in-build facilities for
oxygenating aquarium water.
The critical factor in aeration is surface water turbulence,
which will facilitate the uptake of oxygen (O²) and the
elimination of carbon dioxide (CO²). To some extent,
the way in which this is achieved is irrelevant, as long as
it does not cause injury or stress to the aquarium inhabitants.
Aquarium aerators - more commonly referred to as air pumps
- generally do their job by producing a stream of air, which
is channelled centrifugally or by means of a diaphragm or
by a piston drive, through an air line joined to one or more
diffuser stones or small wooden blocks, which break up the
stream into bubbles as it is forced through the pores of the
diffusing materials. These bubbles create more of an illusion
of aeration that actual aeration, although the smaller the
bubbles - those produced by marine aquarium diffuser stones,
for instance- the higher their aeration qualities as they
rise to the surface. The main benefit derived from bubbles,
however, derives from the surface turbulence they create.
Aquarium aerators - more commonly referred to as air pumps
- generally do their job by producing a stream of air, which
is channelled centrifugally or by means of a diaphragm or
by a piston drive, through an air line joined to one or more
diffuser stones or small wooden blocks, which break up the
stream into bubbles as it is forced through the pores of the
diffusing materials. These bubbles create more of an illusion
of aeration that actual aeration, although the smaller the
bubbles - those produced by marine aquarium diffuser stones,
for instance- the higher their aeration qualities as they
rise to the surface. The main benefit derived from bubbles,
however, derives from the surface turbulence they create.
Air pumps are generally rated either by the volume of air
the produce per minute, or by the number of diffuser stones
they can operate simultaneously in a given depth of water.
Again, as for other items of aquarium hardware, seek professional
advice when you are choosing from the wide selection available.
Filters can also serve as aerators, either because the stream
of bubbles that drives the air operated models rises through
an uplift tube, thus disturbing the water surface, or because
the stream of water produced by electrically operated models
splashes on the water surface - for example, by means of a
spray bar. A growing number if electrically operated filters
(known as power filters) also have an in-built device called
a venture which sucks in air and mixes it with the water stream
as it is driven through on its way back to the aquarium, thereby
assisting with aeration. Venturis are also common features
on power heads, which are electrically operated water pumps
usually fitted to the top of the air-lifts of under gravel
filters.
Filters come in all shapes, sizes and, of course, prices,
but all are designed to sieve out solid wastes from aquarium
water. Most will also perform other functions, such as the
biological purification (detoxification), by means of beneficial
bacteria, of water laden with soluble wastes invertebrates.
Chemical purification is also possible if the filter is of
the canister type. This takes place through adsorption by
means of a suitable medium such as activated charcoal or zeolite
(a clay based material) held in the way of the flow of water
passing through the filter.
Despite the undoubted sophistication of certain models, filters
can be classified into the following categories
Under gravel filters, in which a plate, or set of plates,
or a series o perforated tubes is laid under the gravel of
the aquarium. These filters can be operated using an aerator,
a power head or the flow from a canister type power filter
Box filters, in which the water is driven through a box that
be situated wither within the aquarium itself, or suspended
on the outside. Internal model are air operated, while external
ones can be operated by either air or electricity.
Sponge/foam filters, in which the water is sucked through
a layer of sponge of foam by an air stream from the aerator
Canister power filters, in which water is electrically driven
through a container holding one or more filter media. There
are both internal and external models
Trickle or wet/dry filters, in which water is trickled through
an external medium exposed to the air during at least part
of the journey from and to the aquarium
The main aim of a filter is to maintain water in good condition.
It is this quality that determines whether not a particular
fish, invertebrate or plant will survive. Water quality is
so important that it is safe to say that is we look after
the water, the water will look after our aquarium plants and
animals. It is therefore essential to have a clear understanding
of the process of filtration/purification/detoxification -
preferably before you actually buy a filter.
It is essential to consider briefly the types of filtration
(as opposed to type of filter) and a few of the main types
of filter medium.
Mechanical filtration removes solid particles of waste and
debris from the water. Whatever medium us chosen for the purpose,
it acts as a sieve. Filter floss, sponge, foam, brushes and
many other media are suitable choices, and in the case of
undergravel filters, the gravel itself can act as this sieve.
Chemical filtration removes toxic chemicals such as ammonia
via adsorption (absorption) on to a porous surface. The best
known compounds for this are activated charcoal and zeolite,
although there are others.
WARNING: zeolite removes ammonia and can be "recharged"
by being soaked in salt solution. When this is done, the ammonia
is released into the water. Because of this property, zeolite
cannot be used in marine aquarium, because in these conditions,
it is quite incapable of removing toxic ammonia.
Biological filtration removes dissolved wastes through the
action of beneficial bacteria. The process of detoxification
begins with nitrosomonas bacteria taking in ammonia and converting
it to nitrites, which are also toxic to fish and invertebrates.
Fortunately, nitrobacter bacteria then convert these nitrites
into relatively harmless nitrates. This process is known as
nitrification.
It is also possible, with a little planning and by choosing
the right medium, to keep nitrates under control by means
of other types of bacteria, which will convert then back to
free, harmless, nitrogen that then disperses into the air
at the water surface. This process is known as denitrification.
Just as there are different types of filtration or detoxification,
there are different types of media. One thing that need to
be borne in mind, however, is that clear-cut divisions do
not really exist, in the sense that if a medium is designed,
say, to act primarily as a mechanical one, it will to a greater
or lesser extent - still develop a biological capability over
a period of time as its surface becomes colonized by bacteria.
The extent to which surfaces can be colonized determines how
effective a medium will be in terms of biological efficiency.
When choosing such a medium, therefore, it is important to
consider the percentage of available surface that it contains
for potential colonization, rather than its total surface
area. Gravel, for example, has few, if any, pores and the
available surface area is virtually the same as its total
surface area. In sintered glass media, however. "porosity"
is one of the most important features and it therefore follows
that sintered glass is a much more efficient biological medium
that gravel.
The advantages of sintered glass and of some other biological
media go even further, because the pores that lie deep within
each cylinder, granule or block of medium are exposed to lower
levels of oxygen than the outer ones and can therefore denitrify
as well as nitrify at the same time. As a result such media
are not only efficient at keeping levels of ammonia and nitrites
down but also help in keeping nitrates under control.
For more information on setting up an aquarium Click Aeration
and Filtration
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