Download Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary

Filtration Systems
Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary
FILTRATION SYSTEMS
The natural marine environment, especially the tropical marine environment, is an
incredibly stable one with water chemistry fluctuating by only negligible amounts.
Stability within the natural environment is however conferred by virtue of the
enormous scale and capacity of the natural ecosystem. Stability within a smaller
system requires much more sensitive management and careful balancing of both
stocking densities and feeding regimes against filtration capacity.
Getting the right filtration balance is essential in order to maintain stable conditions
and remove the toxic waste products produced by the tank inhabitants. Aquarium
filtration can be classified as mechanical filtration, biological filtration, chemical
filtration and sterilisation. Filtration systems utilise one of more of these filter types
when maintaining aquarium systems.
Types of Filtration
1. Biological Filtration
The biological filter utilised in the display is contained within the substrate. This filter
bed provides the perfect environment for de-nitrifying bacteria to thrive and is host
to the most important process involved in keeping aquatic creatures alive in the
system. This is the site of breakdown of all bio-degradable waste via the natural denitrifying process known as the nitrogen cycle.
In brief the substrate material has been chosen to present a very high surface area
to volume ratio. The ammonia rich, oxygenated waters present an ideal environment
for autotrophic bacteria to thrive. The various types of bacteria present break down
ammonia, which is highly toxic to marine life, to nitrite, which is far less toxic, and to
nitrate, which is virtually harmless.
The substrate present in tanks is only one way of providing home for the invisible but
essential tank inhabitants. Biological media or filter media and bio balls are added to
the system to provide even more areas for these bacteria to reside. Bio towers
incorporated in designs of some tanks as well as external canister filters can be filled
up with these biological media. They are placed in the areas with the highest
possible water turnover to ensure constant inflow of nutrients (fish waste) to the
bacteria and also to keep them adequately oxygenated. For this reason, filter or
pump should never be off for too long, otherwise all the bacteria die.
1.2 Biological Media
The range of biological media products currently available is immense and one only
has to try which type works the best for the set-up. They all have different texture,
come in different shapes, colours, sizes and often have unique properties, eg. denitrifying, phosphate removing, odour reducing, etc. These are placed into a mesh
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Filtration Systems
Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary
bag and put into an external filter or bio tower along with other types of filter media
(eg. filter floss, which is a type of mechanical filtration) and very often in conjunction
with bio balls.
Picture 1.: Examples of biological filter media. High surface area is owed to porous structure.
1.2 Bio Balls
Bio Balls are plastic balls specially designed so as to provide high surface area versus
volume ratio which gives the bacteria an immense space to colonise. Bio balls also
come in many sizes, colours, shapes and designs. The main advantage of bio balls
over other biological media is that the surfaces are impossible to clog up (when used
with a prefilter) compared to the micropores of porus ceremic filter material. The
reason is simple: the gabs of space within a bioball is large and anything that can
clog it up would already have been filtered by the prefilter (such as filter wool,
sponge, etc). This is the reason why water filteration should always pass through
mechanical filteration (prefilter) before biological filteration. Bio balls also win over
biological media as their high surface area isn´t based on miniature pores. While
these can get clogged up even when a prefilter is in place, bio balls design prevents
this from happening.
Picture 2.: Bio balls come in a wide variety of shapes and designs.
1.3 Cleaning
Cleaning of biological part of the filtration system is crucial and the correct procedure
of doing so should not be underestimated. Bacteria take a while to get established
and removing all parts of the filtration at once or rinsing it with freshwater will kill all
the bacteria. Removing all bacteria leads to catastrophic spikes in ammonia and pH
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Filtration Systems
Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary
and ultimately to mortalities of tank inhabitants. If the filter isn´t designed for partial
media changes, rinse the content in tank water. This way you will get rid of the
material that´s has accumulated on the filter floss, in the pores of biological filter
media or on the surface of bio balls but you will not kill the bacteria.
If you are introducing any type of treatment to the tank, remove the filter from the
system, otherwise the bacteria will be killed. In order to keep the filter running for
the duration of the treatment, fill up a bucket with the pre-treatment tank water and
let the filter running on this small circuit.
Biological filtration on its own cannot support many fish though, and therefore need
to be used in conjunction with other filtration methods.
2. Mechanical Filtration
Mechanical filtration removes particulate waste and other suspended solids from the
tank by trapping them in a fine medium. This medium can be sand, sponge, floss or
wool depending on the size of the display. There are various types of mechanical
filters and many of them also offer habitat for de-nitrifying bacteria and thus
contribute to biological filtration to certain degree. That’s why when it comes to
cleaning, whichever media is used, it needs to be washed in the tank water rather
than fresh water. Regular cleaning to remove the built-up dirt is essential in order to
prevent clogging-up or in the case of sand filters, the sand becoming too compact to
be able to perform its function.
2.1 Pressurised Sand Filters
Among the most complex mechanical filtrations systems are the pressurised sand
filters. These are designed to remove the tank detritus, which is larger than 30-40
micron, much like a sieve works. The filter itself comprises of a container filled with
sand that will filter out the debris as the water flows through it. Sand filters are often
installed with a multi-port valve that makes operating and maintaining the filter
easier. The position of the valve will determine which way the water enters and
leaves the system. The condition of the filter can be also determined directly by the
pressure gauge reading but the range of normality is sand filter specific.
Picture 3.: Sand filter diagram and a multi-port valve.
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Filtration Systems
Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary
The sand bed and associated nozzles/collector laterals/candles on the base of the
filter do not require any direct maintenance provided the plant is operated correctly.
Particular attention should be paid to correct flow rates and backwashing. If the bed
should become clogged due to improper handling this can usually be attributed to
poor backwashing or excessive flow rates. Flows above those recommended will
drive the dirt deeper into the bed, making it much harder to remove, thus requiring
longer backwash.
2.1.1 Backwash
Backwashing is the process of reversing the flow through the sand filter to remove
any dirt trapped in the sand that may be reducing the filter´s efficiency. Without
regular backwashes and maintenance checks, sand filters can become clogged or
concreted, and prone to channelling. If the sand in the sand filter becomes clogged
up and dense, not enough water will be able to flow through it and this consequently
may affect other equipment plumbed onto the system, eg. inline heaters which need
sufficient flow through them otherwise they will switch themselves off. In a scenario
like this, quality of the entire system may become compromised and the filter is not
functioning properly and a heater in not heating up the tank water.
On smaller filters with a multiport control, the pumps must be stopped before the
valves are adjusted The valve arrangement on the sand filter should first be moved
to the backwash position then the filter should then be run for 5 to 7 minutes or until
the filter has been completely flushed free.
Picture 4.: Diagram of sand filter indicating the direction of water when filtering and when backwashing.
2.1.2 Rinse
After backwashing is completed, the multi-port valve should be moved into the
´rinse´ position. This means the water will flow through the filter as though it was
filtering but this time the water will be sent to waste instead of being returned to the
tank. This ensures that any residual material that wasn’t removed during
backwashing is removed now from the system. Rinsing should take 30seconds to 1
minute maximum.
The pressure gauge should then be rechecked to ensure that the filters have been
cleaned and the procedure repeated if necessary.
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Filtration Systems
Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary
2.2 Under Gravel Filters
Under gravel filters are an early form of filtration, however still popular as it is
relatively cheap, easily available, yet very efficient.
The base of the tank is covered with a plastic plate that has fine slits cut into it and
this tray is covered by gravel. A tube leads from this tray, up the back corner of the
tank, with an airline inside the tube. As the air rises in the tube it creates suction
which draws the water through the gravel bed. Gravel bed in this case acts as filter
media and thus harbours purifying bacteria. In order for this type of filtration to work
properly, the gravel needs to be siphoned regularly to prevent clogging up of the slits
on the gravel plate and also the prevent gravel residing bacteria from starvation of
dissolved oxygen.
It is important to limit the amount of decoration you put over the gravel plate, as this
limits the flow and inhibits the filtration. It is also essential to ensure that the filter
plate is completely covered at all times, as any gaps in the substrate or exposed
plate will reduce the efficiency.
The biggest drawback with an under-gravel filter is the potential for algae growth in
your aquarium is increased. With all of the organic matter being trapped in the gravel
with water passing through, the nutrients are redistributed into the water column
feeding the algae.
Picture 5.: Schematic diagram showing the direction of water flow through the filter plate.
3. Chemical Filtration
3.1 Carbon
Chemical filtration refers to any filtering substance that is designed to change the
chemical composition of the water, but most often refers to the use of activated
carbon or other cleaning resins. Activated carbon pulls dissolved organics from the
water by adsorbing them. Carbon is very effective in removing a variety of impurities,
such as copper, chlorine from tap water, dissolved proteins and carbohydrates,
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Filtration Systems
Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary
heavy metals and ions, medications, etc. Removing all these substances from the
system will make the water look crystal clear
Activated carbon is made from various base materials that have been heated then
steam-treated. The steaming process makes the carbon extremely porous. Porous
substances have extensive surface area. As the water passes over carbon, the
carbon chemically attracts pollutants that adhere to the surface of the carbon,
including odours and colour.
Since carbon works by chemically attracting pollutants to its surface, once the
surface area is covered with dissolved organics, the carbon is exhausted and must be
replaced. Depending on many factors, this can happen anywhere from a few days to
3-4 weeks. One signal that your carbon is exhausted will be a gold tint to the water.
Picture 6.: Carbon pellets and process of molecular binding to carbon.
3.2 Zeolite
Chemicals such as zeolite can be used in emergencies to remove ammonia from
displays, but should not be used long term as it can destroy the natural bacteria
needed to cycle the tanks.
3.3 Protein skimmer
A protein skimmer or foam fractionator is a device used mostly in saltwater aquaria
to remove organic compounds from the water before they break down into
nitrogenous waste. Protein skimming is the only form of aquarium filtration that
physically removes organic compounds before they begin to decompose, lightening
the load on the biological filter and improving the water's redox potential. Although
the process of foam fractionation is commonly known for removal of waste from
aquaria, it is, in fact, a rapidly developing chemical process used in the large-scale
removal of contaminants from wastewater streams and the enrichment of solutions
of biomolecules.
Protein skimmer removes certain organic compounds, including proteins and amino
acids, by using the polarity of the protein itself. The water flows into a chamber
containing millions of tiny air bubbles. These bubbles get coated in the protein rich
water as they rise up through the chamber, and as the collect at the top they are
pushed into a collection cup. The collection cup can be emptied and cleaned
periodically, removing waste from the system.
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Filtration Systems
Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary
Effectiveness of the system can be maximised in several ways. The smaller the air
bubbles in the chamber, the greater the surface area versus volume ratio and thus
more compounds can be bound onto the air bubbles and subsequently removed. The
length of time the air bubbles are present in the chamber of the skimmer also
increases effectiveness. Foam collected in the collection cup should be as dry as
possible as to decrease the amount of water removed from the system when
emptying the cup.
Picture 7.: Schematic diagram illustrating the function of a protein skimmer.
3.4 Ion exchange resin
These filter media are less utilized than carbon, but are becoming more common.
These work by attracting a specific molecule to adhere to them. Some attract
ammonia or nitrate, and some remove dissolved organics. Ion exchange resins are
also utilized in some carbon mixtures available on the market. The resins often
strengthen the filtering ability of the carbon, as well as help biological activity by
removing pollutants before they enter the nitrogen cycle.
There are different methods to "chemically" treat the water. There are many
different media that you can use in the chemical filter, and in different applications.
Some of these chemicals include: carbon, zeolite, peat moss, calcium hydroxide,
poly adsorption pads, and other chemically treated media. There are also many
other additives, and vitamins to aid in supplementing the efficacy of the chemical
filtration.
4. Sterilisation
Ultraviolet light can be used in addition to biological, mechanical and chemical
filtration. The UV light denaturates the DNA of free bacteria and pathogens as they
pass through the filter. It also significantly reduces the risk of disease spreading in
the tank and eliminates the risk of toxic tank syndrome caused by sudden bacterial
or algal blooms. This was the UV filtration provides a measure of insurance against
mismanagement of the aquarium system, however all efforts must be made to
employ other types of filtration. Water passing through the UV filter must be clear in
order for UV light to penetrate and for sterilisation to be effective.
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Filtration Systems
Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary
Picture 8.: UV light denaturates DNA at wavelength approx. 250-270nm. The peak wavelength of 264 nm is the most lethal to a
living organism’s DNA, and prevents it from reproducing.
Picture 9.: UV Steriliser mechanism
5. Filter Maturation
Populating a filtration system with a colony of denitrifying bacteria is called cycling
and this process is essential for a correctly functioning tank. Brand new system can
be colonised by these microorganisms in several ways, which can also be used all at
the same time.
5.1 Cycling
If possible, gravel or substrate for another already populated, established and
healthy tank can be used to speed up the process. This will seed the biological filter
bed with the helpful bacteria and will accelerate the maturation of the biological
filtration process. Establishment of de-nitrifying bacteria will take place naturally,
without seeding, however the maturation process will take longer.
The next stage is to introduce a source of organic waste. These pollutants are an
essential food source for the bacteria and this starts the process of the nitrogen cycle
when harmful ammonia is broken down to decreasingly harmful chemicals.
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Filtration Systems
Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary
There are several methods of how to start the cycling process. Fishless cycling
involves using household ammonia or a designated aquarium waste substitute that
mimics pollution. Adding biological starter fluid, powder or a capsule is known as
seeding. In the case a gravel from a mature tank has been used, this step can be bypassed, however it can be carried out regardless.
Cycling that relies on hardiness of some fish species to withstand poor water quality
for the period of time the denitrifying bacteria need to establish themselves in the
system, is called fish-in cycling. This means that the first pre-mature tank inhabitants
are exposed to varying and often high levels of ammonia and nitrites and actions like
this can rarely be justified. These fish, just like any fish, produce nitrogenous waste
on which bacteria can feed and in return they will establish themselves in the
system. Adding bacterial food source without adding bacteria is known as ´feeding´
the filter.
Process of tank maturation follows certain pattern. In a closed system there will be a
steady rise of ammonia whose levels will drop in conjunction with a rise in nitrite.
When the level of nitrite collapses the filter is mature.
Picture 10.: Ammonia, nitrite and nitrate levels changes during tank cycling period.
To complete this process may take 2 to 3 months (3 to 6 weeks with quick maturing
agent), throughout which time there is a very high risk to less hardy creatures. In a
closed system only hardy creatures can be kept throughout this period and stocking
densities must be kept low due to the toxicity of high nitrite levels.
In an open system with regular water changes maturation process can be speeded
up, however this also depends on the temperature of the tank. Cold water systems
need more time to establish a fully functioning bacterial colony, while warm water
systems are more efficient in this. Frequent water tests have to be carried out during
an aquarium cycling to monitor the maturation process.
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Filtration Systems
Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary
5.2 After cycling
After the tank has matured, regular water tests still have to be carried out in order to
ensure the ammonia and nitrite levels stay at an acceptable level. See the table
below for guidance on normal, acceptable and critical levels of these harmful
chemicals.
Ammonia
Nitrite
Nitrate
Normal Level
0.1ppm
0.0ppm
0.0ppm
Acceptable Level
0.2ppm
2.0ppm
2.0ppm
Critical Level
0.4ppm
4.0ppm
20.0ppm
If critical levels are reached on any of the above then a substantial water change
must be done immediately to reduce the level to an acceptable one. Obviously it is
preferable to maintain the above components between normal and acceptable levels
by initial small frequent water changes rather than let them rise to critical levels
which may necessitate water changes of up to 50%.
5.3 Ammonia and pH problems
The massive increase in bacterial activity has the effect of depressing pH levels and
this is a common problem in newly set tanks. Although hardy creatures will tolerate
low pH for some time, the more delicate creatures may require a minimum pH value
of 8.1. This will be maintained throughout the filter maturation process by regular
water changes. pH stability will however ultimately be stabilised by virtue of the
inherent buffering capacity of natural décor such as the calcium based substrate in
most saltwater displays.
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