One of the most crucial equipment for an aquarium is the filter. In fact, filtration is one of the key components for a thriving aquarium. This is because it helps prolong or delay the aquarium water from turning foul. Bear in mind that in their natural habitat, fishes live within a large water volume that is constantly being replenished. Any decaying debris or wastes produced by all things living in the habitat will not pollute the water. This is because the large body of water simply dilutes everything.
However, the same cannot be said about a controlled environment like in a fish tank. Fish wastes and decaying plants will rapidly pollute the tank water. This results in high ammonia levels which turns the tank water toxic if it is left unchecked.
Any kind of filtration performs three basic functions in order to keep water quality good for fish to thrive in.
Mechanical Filtration:
This process helps remove any debris, fish wastes or uneaten food from your main tank by
the filter media. Such media includes sponges and filter wools that trap and prevent debris or dirt from circulating back into your aquarium. It must be remembered that such media do get clogged over time and must be replaced eventually (within reasonable time). Too much trapped debris slows down water circulation and could be detrimental to your fishes or can affect general water conditions.
Please note that not all debris or dirt can be sucked up by the filter. Floating dirt or particles still visible in the water, in particular, should be manually removed with a water change or scooped up with a net. Otherwise, if there is debris lying on the substrate, use a hose or gravel vacuum to siphon – whichever is applicable.
Biological Filtration:
This is the process of cultivating and maintaining the beneficial bacteria that helps convert
ammonia (NH3) into nitrite (NO2) and nitrate (NO3) – please refer to article on Nitrogen Cycle. Beneficial bacteria requires oxygen and ammonia. Thus, any filtration with a steady water-flow rate will produce oxygen within the aquarium (note: adjusting the filter outflow to agitate the water surface or using an air pump oxygenates water also). Ammonia is supplied by fish wastes, decaying plants or uneaten fish food. When both oxygen and ammonia is present, bacteria will multiply by clinging on to any parts of your aquarium like the sand bed/substrate, rocks and even on the glass surface.
However, the bacteria count would usually be insufficient, which is why, a filter media that aids their propagation is necessary. These media include bio-balls, ceramic-rings, coarse sponges and others.
Chemical Filtration:
The process of removing dissolved chemicals that are not visible – like protein and organic
compounds. For this purpose, activated carbon is used because it is very efficient in absorbing chemicals and dissolved organics, clearing them from the water. It also removes any bad odour present. Please note that activated carbon will also absorb chemicals like fertilisers and fish medication. Therefore, the activated carbon needs to be removed before administering these chemicals. Otherwise, the efficacy may be reduced. Activated carbon must be replaced once its surface area has been covered although we are not able see this taking effect, replacement once every 3 to 4 weeks is a good guide to follow. An indication of when extensively used activated carbon needs replacing is if there is a golden tint in your aquarium water.
Some basic units of filtration:
Here, we take a look at some of the very common types of filters suitable for aquarium setups.
The Sponge Filter
Sponge filters are very common. It works by sucking water through sponges on the filter while
the whole unit is submerged in the aquarium. There are readily available inlets for air tubing or
an external powerhead to be attached on top of the unit. Water is sucked in through the sponge
and is extracted using an attached powerhead, or via the inlet air tubing with the air bubbles
blowing out. Bacteria would be easily cultivated on the pores of the sponges. A rather cheap and
effective way of biological filtration, but does not do well with overstocked aquariums as they
are less effective in mechanical filtration and serves little or no purpose in terms of chemical
filtration. It is a very good form of filtration for tanks with low bio-loads – like a growing-out tank
for fries.
Mechanical Biological Chemical
The Box Or Corner Filter
Also known as bubble filters, these filters are boxed shape, with an air-tubing inlet. Cotton wool normally comes together as the filter media. Designed to have water running through the cotton wool, where it traps debris and provides a good place for beneficial bacteria cultivation. Apart from the cotton wool, these units come with some sort of sand or pebbles.
The purpose is to add weight to the filter so that it will not float. Similar to sponge filters, the box filter uses air pumped into the unit to create an ‘air lift’. The bubbles draw water up to the surface of the aquarium. This oxygenates the water and creates water circulation through the filter. While simple, the box filter does have limitations. With a small filtering capacity and clogs rather quickly, this kind of filter is best for small tanks with a few fishes.
The Undergravel Filter (UGF)
As the name suggests, this type of filter is placed at the bottom of the aquarium, under the substrate or stones. And this is where beneficial bacteria are cultivated. The filter comes with what is known as a
‘plastic diffuser’, usually in square plate sections. These filter plates can be joined to cover an area of the tank bottom, depending on the size of the aquarium. There is also a plastic pipe that extends upwards
- mounted to the filter plate that is placed towards the back corner of the tank. Within this pipe, an air tube is inserted. Again, with the principle of ‘air lift’, water is sucked though the substrate, down past
the filter plates beneath and lifted up through the plastic pipe as the bubbles rise in the pipe. Beneficial bacteria colonise the filter plates at the bottom of the tank. Some people attach an internal power head
to the upward pipe for a higher or faster flow rate – increasing water oxygenation. This type of filter is only good as a biological filter. To some degree, it also acts as a mechanical filtration.
But, like all filters, there will be tendency for clogging or malfunction in which case, the whole tank needs to be torn down. Without saying, maintenance of this filter can also be extremely cumbersome.
These filters usually come with a power head of a reasonable size, and small detachable
compartments to insert various filter media. A simple and efficient method of plug and
play. The whole unit is submerged into the aquarium. The built-in powerhead sucks
in water through the media-holding compartments and water is sent out through an
outflow nozzle that can oxygenate the water. A relatively newer form of filtration, the
internal power filters come in different sizes with different flow rates. Choose one that
best suits your aquarium size. Please note that actual flow rates of these filters are
normally lower than what is stated on the box packaging. The only downside of these
filters is it might increase your tank temperature. Therefore, these filters may not be the
suitable (but, does not mean it cannot be used) for situations when you are trying to
achieve lower water temperatures – like shrimp tanks or planted tanks.
Overhead Box Filters
These filters are rectangular boxes placed on top of the aquariums. Each filter comes
with a submersible powerhead and has a rubber/plastic tube or pipe attached. The hose is connected
to one end of the filter box. Within the box are divided compartments where you place the filter media.
At the other end of the box is an outlet where the water flows down and back to the aquarium.
Such filters have an advantage of having larger storage capacity for media compared to internal power filters. An overhead box filter can be unsightly though. Such units usually come with powerheads of different rating and boxes of different sizes. Again, choose the size that is suitable for your aquarium. Like the internal power filter, the submerged powerhead can raise water temperatures, and as mentioned may not be quite suitable in certain cases where lower temperature is required.
External Hang-On-The-Back Filters (HOB)
This is an oddly-shaped box with a plastic inlet tube that extends below the water surface to suck in aquarium water. The HOB is designed to hang to the back or the sides of the aquarium.
With a relatively small flow rate and limited media capacity, HOB filters are only suitable for aquariums not larger than 75 gallons and are not suitable for tanks with large amounts of fishes.
Wet/Dry Trickle Filters
Such filters are usually self- or custom-designed and have proven to be quite popular
with marine hobbyists in previous years. The concept of this filter is to have the tank
water mix with lots of oxygen (by exposing to air) to encourage aerobic function.
Aerobic here, simply means the cultivation of bacteria or life with the presence of
oxygen. This filter works well with high levels of oxygen present on the drip tray which
is often left damp, despite the name Wet/Dry Trickle Filter. It works with a pre-filter or
the first chamber, filled with a cotton pad/floss. The next stage or chamber would have
some sort of chemical filtration media like activated carbon. Water is trickled down to
the damp, drip tray. This is where the beneficial bacteria, nitrate (NO3) are cultivated in large volumes. The water which collects on the drip tray then falls into a sump which has a pump to deliver water back to the aquarium in volumes equal to the drop zone. There is a type of stackable, overhead wet/dry trickle filter that serves the same function.
External Canister Filters
These are the cylinder-shaped filters that stand vertically. Attached to the canister are two
hoses which are for the inlet and outlet. Located on the inside top of the canister is a pump that
generates the suction to get tank water to pass through the canister. Within the canister, there is
a series of stackable/detachable trays for filter media. Water is sucked into the canister and flows
through the media trays before being pumped back into the tank via an outlet hose. The canister
is placed outside the aquarium with the attached hoses dipped into the aquarium. The canister is
considered to be the most popular type of filtration in recent times and has proven to be reliable.
The Sump Tank
This type of filtration system is similar to the wet/dry trickle filter. It is designed and placed underneath the aquarium tank. Within the sides of the aquarium is a full-height glass partition with a gap near
the top that allows water to drop into the compartment. Located inside this partition is a hole that has been drilled right through the aquarium bottom, with piping connected to the hole. Water entering the partition will flow into the piping and channeled into the sump tank. The sump tank is usually divided into compartments to be filled with media such as cotton wool, bio-balls, ceramic rings and activated carbon.
In the last compartment, a pump connected with piping will draw water from the sump back into the aquarium, thus creating a flow. A very efficient filtration system because it can store large volumes of water in the sump and cultivate large amounts of beneficial bacteria.
Filter Media
At this point, we shall look at some common types of filter media and their uses.
Cotton wool/floss – usually a media placed in the first compartment, as a mechanical filtration. It helps remove debris and floating particles by trapping them while the water is flowed back to the aquarium. This media is usually replaced with new ones during water changes or filter maintenance.
Bio-balls and Ceramic Rings
This is a homing media used to cultivate beneficial bacteria. Bioballs are actually plastic balls with prongs for bacteria to attach to. Ceramic rings serve the same purpose. They have very rough surfaces and when placed into the filter, the rings overlapping one another create crevices for cultivating bacteria. Maintenance or cleaning of such media is only carried out periodically.
Please note that when cleaning these sorts of media (bacteria-homing type); only use the existing aquarium water. Rinsing them with tap water which contains chlorine will kill the beneficial bacteria already living
in the media.
Activated Carbon – as mentioned earlier, this is a form of chemical filtration. It is good for removing chemicals and toxins such as protein or other organic compounds. In manufacturing this media, tiny pores are created. These pores, together with carbon compound can trap dirt and remove odour in the tank via ion-molecular exchanges.
Peat – this media is usually added to the filter to soften water hardness. Peat is actually an organic material. Usually made up of decaying leaves/plants and vegetation or, any other organic material that normally forms in acidic conditions. Depending on the type of aquarium setup, peat is often used in South American biotopes or for fishes that prefer soft, acidic water.
Coral Chips
As the name suggests, coral chips are actually broken chips of dead coral found in the sea. It acts as a buffer to achieve higher pH values and hardwater conditions. Since it is naturally from the sea – where water conditions are alkaline – it proves to be a good filter media that can maintain water hardness and increase pH. Used most suitably in rift lake setups, as well as marine tanks.
