Types of water filtration in the aquarium

An aquarium is an imperfect micro-ecosystem imitation of the natural world. But aquariums are often more densely stocked with fish than the natural environment.

Fish produce waste with their excrement and breath. Another source of waste is uneaten food or plant debris.

These waste products accumulate in the tanks and end up polluting the water. As the degree of contamination increases, the health risk to aquariums increases and contamination removal becomes critical.

Filtration is a common method used for maintaining healthy aquariums. And today we are not going to see the types of water filter for fish tanks, we are going to stop to see what kinds of filtration you can find in them.

Next, we are going to see how the different types of filtration work, and the advantages and disadvantages of these types of aquarium filtration.

Three types of filtration

There are three types of filtration that are used in aquarists to maintain the good health of any aquarium:

mechanical filtration

To accomplish this, the aquarium water is forced through a medium that is designed to trap and hold these tiny physical debris particles until they are cleaned.

Within the accessories for fish tanks and aquariums, this type of filtration is available in many forms, including different types of foams, sponges, pads, paper pleats…

In order for it to work properly, it is important to clean this medium regularly to remove the particles it has been trapping, before the residue begins to break down and ends up returning to the aquarium.

As long as the debris remains in the filter material there is still a negative impact on the water. As the waste breaks down, it increases the level of nitrates, phosphates and other harmful chemicals that accumulate in the water and decrease the quality of the water.

In this way, the water remains crystal clear, giving the impression that the filter is still working well, although in reality it has a negative effect on the quality of the water and therefore also on the fish.

That is why maintenance and cleaning of filter media is a must.

Placement of mechanical means

Large media should be the first load the water encounters in the filter stream. After that point, finer mechanical media can be put on.

There is no point in adding a large pore media to the filter if the water has already passed through a finer media because it will trap almost nothing, if anything. Of course, it will become a medium colonized by nitrifying bacteria.

Keep in mind that every tank is different so on some tanks the fine media will pick up a lot of debris while the course mechanics look new and clean, on other tanks the opposite will be the case.

Error of oversizing the mechanical filter

Over time, all mechanical filters end up getting clogged with particulate matter. When this occurs, it will cause the water flow to slow down or flow around the material instead of through it. At that point, the hobbyist should recognize the need to clean the filter.

By oversizing the mechanical filtration media, it can take months before the filter loses its efficiency, which means months between cleanings.

Although the aquarium appears clean and free of particles, the filter will contain large amounts of detritus (small pieces of decomposing plant or animal material) and other debris that slowly break down and contaminate the water with toxic products such as ammonia, nitrites and, ultimately nitrates.

So even if the filter is not so clogged that it has reduced flow or stopped working, it is degrading the quality of the water.

Mechanical filter under pressure

In this type of filtration where the mechanical media is open, the water passes through the mechanical media under the force of gravity only.

Because it is not under pressure, the water simply passes around or over it when the medium is clogged. This means that although the filter is working, the water is not being cleaned because it is bypassing the mechanical means.

biological filtration

Biological filtration is the term used to describe among the different types of filtration the action of beneficial bacteria, which are established during the initial cycle of the aquarium. These bacteria break down toxic compounds into less toxic compounds.

These bacteria require a surface to adhere to as well as oxygen-rich water.

Biological filtration is essential and needs to be properly established in each aquarium in what is known as aquarium cycling.

When the aquarium has been cycled, and biological filtration established, the different types of bacteria convert the toxic chemical by-products produced by the aquarium inhabitants into less toxic nutrients.

This process of breakdown by bacteria is called the Nitrogen Cycle.

Cycle of nitrogen

In the Nitrogen Cycle, the waste products of fish, plants, and invertebrates, along with any dead organisms or uneaten food, are broken down by bacteria and fungi into ammonia.

Ammonia is extremely toxic to all aquarium inhabitants, and is broken down into nitrites by an oxygen-loving bacterium known as Nitrosomonas.

Although nitrites are not as toxic as ammonia, even at low concentrations in the aquarium they can be harmful to fish and invertebrates.

Again, another bacterium called Nitrobacter, which also uses oxygen, acts in a similar way to Nitrosomonas, essentially transforming nitrites into relatively harmless nitrates.

Nitrates, at low to moderate levels, do not harm most fish or invertebrates, but can be the source of some unsightly algae problems if not controlled by both chemical filtration and water changes.

In the natural environment, these nitrates are taken up by plants as fertilizer and this occurs to some extent in an aquarium planted with real plants. If you are interested in live plants, you may want to take a look at our guide to the planted aquarium for beginners.

But for the nitrate level not to build up to a harmful level, regular partial water changes are required to remove the nitrates and introduce new, uncontaminated water.

Nitrogen cycle and the biological filter

These nitrifying bacteria that consume ammonia and nitrite will live on surfaces where conditions are ideal. This means that the ideal temperature, oxygen level, and food supply will favor these bacteria.

In an aquarium the temperature is generally uniform and aquarium lighting is not a major factor, so this will not affect where the nitrifying bacteria will colonize.

However, oxygen levels and food availability will greatly affect nitrifying bacteria colonies.

These bacterial colonies take several weeks to form, and an aquarium needs to «mature» that colony of bacteria before introducing fish.

This is what is known as cycling the aquarium, that is, waiting for the bacteria colonies to establish a clean and stable environment for the fish. If you have any questions, you can refer to Aquarium cycling step by step, our article dedicated to this important topic.

biological material

Live rock and sand are biological filtration material as they harbor a good amount of nitrifying bacteria. In theory, an aquarium can be maintained with this type of biological filter only. However the aquarium population would be restricted to small numbers.

The bacteria colony sits on the glass in a corner or on the gravel, but the same amount of food and oxygen does not get there as when they are in a biological filtration medium where there is a constant flow of new nutrients and oxygen.

This is the reason why nitrifying bacteria are favored to colonize the surface that provides the biological filtration medium on the filter.

In most cases, the primary biological filter is nothing more than a chemically inert, porous sponge, providing a large surface area on which bacteria can grow.

Still, there are different forms of biological filtration media, and the surface of the material is the key.

surface and oxygen

Bacteria need to be exposed to water, so the more surface area available to biological material, the more bacteria can establish. Maintaining a continuous flow of water will provide the necessary nutrients for them.

On the other hand, oxygen levels are frequently the limiting factor for maximum biological filtration efficiency.

If the oxygen level in the water is high enough, external filters and other submerged media filters can be very effective.

Filters in which the biological medium is exposed to the air will have the highest efficiency. However, submerged media filters typically require much more surface area to compensate for the relative lack of oxygen and be as effective as other forms of filtration.

Wet -dry filtration and other forms of biological filtration that expose the media surface directly to the air are a very efficient way to ensure high oxygen levels because there can be up to 20 times more oxygen in air than in water (thanks a lot, Ernest ).

By briefly exposing the bacteria to this oxygen-rich environment, their efficiency is greatly increased.

Biological Filter Maintenance

This usually means lightly rinsing the medium with fish tank water when residue deposits are visible on the medium and nothing else.

On the other hand, when it is necessary to medicate the fish it is recommended to use a separate tank (hospital or quarantine tank). When antibiotics (antibacterials) are used, the extensive use of these drugs, we will kill off harmful bacteria, but also friendly nitrifying bacteria.

chemical filtration

Chemical filtration removes unwanted or toxic chemicals as the water passes through a chemical medium or resin.

It can be used to remove odor or discoloration, but in either case it is a symptom and the cause needs to be treated.

The only other use for chemical filtration is drug removal.

There have been a number of advances in recent years, giving us new products that are aimed at removing specific chemicals or excess nutrients from the water.

Used correctly, these media can be incorporated into filtration to improve water quality and reduce the amount of maintenance and water changes required to maintain a healthy aquarium.

However, it is important to carefully monitor the water chemistry and perform water changes as needed.

active carbon

There is a wide range of quality levels in coal. And as is often the case with everything, you will get what you pay for, meaning higher quality charcoal will be more expensive.

Coal doesn’t last forever. The lifetime of the carbon depends on several factors, such as the quality and quantity of the carbon used, the amount of chemicals in the water, the flow the carbon receives, etc.

Best practice is to replace the carbon monthly during the monthly filter cleaning.

Many aquarists avoid using charcoal on a regular basis because it can remove some beneficial substances such as some trace elements needed by fish, corals and aquarium plants.

If proper water changes are performed, the use of charcoal in the aquarium filtration system should not be necessary.

Lastly, many aquarists use the carbon for 24-48 hours once a month. This removes harmful substances without constantly removing the good ones.

Types of aquarium filters

Conclusions on the types of filtration

The filtration system is responsible for keeping the water clean and free of debris (tiny bits of plant material, food scraps, feces, fish residue, etc.) and toxic compounds that are dangerous to the inhabitants.

Knowing the three types of filtration used in the aquarium is vital to advancing as an aquarist.

It is necessary to know the importance of biological filtration on which the balance of the ecosystem recreated in an aquarium is based. Understanding the Nitrogen Cycle is critical to understanding how biological filtration works.

The need to use mechanical filtration to remove solid debris before it begins to break down is another key part of a fish tank’s filtration system, and regular cleaning is the foundation for a healthy aquarium.

Finally, chemical filtration must be a punctual resource, in which specific substances are removed at certain times.

Remember that all the filtration in the world can be undone by insufficient water changes. Filtration does not and cannot compensate in any way for the lack of water changes.

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