If you imagine your aquarium to be a house, the filtration system is a hardworking janitor who works 24/7 to keep everything clean.

No matter how beautiful and impressive your setup may be, without an effective filtration system it will eventually become dirty and ugly, it is important to install an effective filtration system for your aquarium. 

Exhibit A - ugly, unfiltered fishtank

Exhibit A – ugly, unfiltered fishtank

Exhibit B - dirty, unfiltered fishtank

Exhibit B – dirty, unfiltered fishtank

  Any living organisms in an ecosystem, whether it is fish or aquatic plants, will naturally produce large amounts of waste through excretion (using the bathroom) and respiration (living).

  Although other methods such as decomposers and bottom-feeders can be used to keep the tank clean, a good filtration system is an absolute must to keep your setup healthy for your fish and your eyes.

  There are two main types of different filtration mechanisms – chemical filtration and mechanical filtration. 

  Mechanical filtration pumps water through a screen which restricts the flow of a certain size of particles, the filtrate (dirty, unwanted material) is physically blocked by a fine filter mesh.

  The biochemical filtration process is often used to filter smaller particles which cannot be trapped by mechanical methods by changing the biological structure of the particles – not only does this get rid of the filtrates, they can sometimes even be converted to chemicals which are beneficial to your aquatic ecosystem.


 There are a wide variety of different materials that can be used for aquarium filtration. The most popular and cheapest option are known as “filter wools”. 

Not from the wool of a sheep!

Not from the wool of a sheep!

Made from Nylon - an artificially created wool-like material

Made from Nylon – an artificially created wool-like material

This wool is made of a material called polyethylene terephthalate (commonly known as nylon).

Nylon is much more durable than the wool of a sheep, it will last for much longer. Nylon is also more chemically & biologically inert, it will be less prone to

There are many other different types of synthetic materials include: ceramics, sintered glass, silicon products and igneous gravels.

Ceramic Filter

Surface area is a very important, materials with a large surface area allows for more water to pass through, increasing the filtration efficiency.

Usually, aquarium filters are never purely mechanical and always have some sort of biological function to prevent bacteria growing and clogging the pores of the filter. Porous materials like activate carbon and zeolites added to the filter.

activated carbon – filtration mediums come in all forms!

The most basic aquarium filter has filter wool and activated carbon. The filter wool removes large particles and the activated carbon adsorbs (not to be confused with absorbs! Adsorbs means that it is held on the surface) the smaller particles which are left behind. Xxx Although this is an efficient system, the filter and wool must still be changed at regular intervals.

If an activated carbon filter is not replaced regularly then it will release the adsorbed particles back into the environment in very large doses, if it is allowed to be saturated without replacement. Unfortunately, activated carbon can’t be simply replaced by boiling in water or heating wave. If you had access to a military-grade laser beam or any other method which can heat the activated coal to temperatures of 500 – 900 degrees then they can be thermally regenerated. Fortunately, activated coal is very cheap and easy to replace.

Types of filters:

POWER FILTERS (most commonly used and easiest to replace)

HOB (hang on back) filter

These filters are called “HOB – hang on back” filters which cling to the edge of the aquarium wall. These filters are powered by a spinning propeller fan called an “impeller” which pushes water from an aquarium into several different layers of waters for cleaning before being pushed back.

Depending on your requirements, you can use many different types of filters in a HOB filter for your aquarium. It will be very easy to clean a HOB filter without disturbing the fish in the tank because it is placed outside of the living environment. The disadvantage of the power filter is that they are quite loud, due to the rotor vibrations – this may be loud for both your fish (if you are keeping highly sensitive species) and yourself & friends/family (you’ll have to keep it in the lounge, not your bedroom!).

CANISTER FILTERS (larger capacity than HOB filters)

Unlike a HOB filter where the water flowing back into the tank can fall through the air, a canister system is fully sealed. This means that the water in the aquarium, intake/output tubes and canister are all joined into a single body of water. This adds an extra layer of protection to your aquarium system by preventing anything from outside the tank entering the water.

Image result for canister filter aquarium forums

The main advantage of canister filters compared to HOB is they provide a much greater choice of filtration material in both range and combination. There is an intake pipe at the bottom of the canister through which water enters, the water passes through the filter material inside the canister filter and comes back through the other side through the pipe returning the water. This filter works by a very clever siphoning system which relies on gravity to save electricity and power.

A huge benefit of a canister filter is that it does not reduce the space available inside your tank because the large filtration unit sits outside. This also allows for a larger filter capable of handling greater loads because the weight does not sit on the fish tank.

Because the canister sits outside of a fish tank, another huge advantage is added, installation of other aquarium equipment is alowed, such as water heaters and carbon dioxide diffusers. Some equipment can be removed the tank and installed directly into the return pipe of the filter.

However, canister filters come with their challenges too. First of all, they are more expensive to buy. Secondly, they are harder to clean than power filters due to the tight concealment of the pipes needed to maintain a clean, fully sealed system to keep your aquarium clean.


Another type of filter is called a “trickle filter” or “trickling filter” or “wet/dry filter”. The most common type of trickle filter is placed at the bottom of the aquarium, some trickle filters are placed at the top.

Trickle filter placed at top of aquarium

Sometimes a wet/dry filter can be placed above the tank. Water is pumped over several perforated trays filled with nylon wool, gravel or another material. This wool is kept wet constantly which lets helpful bacteria grow and help filtration through their aerobic respiration processes. The water then returns to the aquarium like rain.

Usually, the wet/dry filter is placed at the bottom of the tank. With this design, gravity forces the water to be fed to the filter below the aquarium. Pre-filtered water is sent to a drip plate. Pre-filtration occurs in the aquarium through a foam block, overflow sleeve or siphon weir, or it may simply be prefiltered by filter wool sitting on the perforated plate. The unfiltered dirty water from the aquarium spreads all over the drip plate and rains down to the bottom through some sort of medium. This medium can be filter wool or a plastic sheet rolled into a spiral like a mosquito coil ( DLS “double layered spiral” ). Another popular medium is a bunch of “bioballs”.

As the water flows over the filtration materials, oxygen is gained, carbon dioxide is released, bacteria transforms the waste materials into less-harmful, sometimes beneficial materials which is fed back into your aquarium. In the final stage, water enters the sump of the filter. You can do a lot of customisation to the sump, it can contain many compartments for different accessories, such as heaters and thermostats.


 In my opinion, algae filters are one of the most interesting ones there are because you are filtering the water by introducing another living, breathing organism into the environment. Algae filters allow your aquarium to operate just like in the wild, you capture every section of mother nature into the beauty of your own fish tank.

Algae filter (from Michael Langerman’s yutube channel)

Here’s a video of how it works

 One major problem faced by owners of algae filters is the growth of harmful outside bacteria which causes disease for your fish and algae filter. Although the harmful bacteria can be killed with an ultra-violet light (the same as sunlight) the problem is that the UV light will kill the helpful bacteria too. Therefore, UV should be only be used when absolutely necessary.

Fluidized bed filter 

Image result for man drowning in quicksand funny

A fluidized bed filter (FBF) sounds complicated, but this type of filter works just like quicksand.

The idea is to direct water so it flows through a sand bed from below so the sand behaves like a liquid. (this is exactly how quicksand works) Sand has a very large surface area so as the water flows through bacteria will be trapped between the sand particles.

A FBF aquarium filter can be very easy and fun to build yourself.


One of the oldest types are undergravel filters. An undergravel filter has a porous plate which sits underneath the gravel on the base of the aquarium with one or more uplift tubes.

Usually undergravel filters are simply powered by air displacement. Air stones are placed at the base of the uplift tubes. The air stones create negative pressure and force water out of the uplift tube through the medium. After that, water filters through the gravel which acts as the filtration material.

A higher flow rate of the water through the gravel can be achieved by using a water pump instead of air displacement.

The gravel is colonized by good bacterial which provides biological filtration for your aquarium. With underground filters, the substrate of your aquarium can double as a filter!

Detailed Undergravel Filter Diagram

Undergravel filters come with a potential problem – they are not good for underwater plants. Fine substrates such as feces, sand or peat may clog the undergravel filter. Once the filter is clogged, the entire substrate must be removed for easy cleaning, this will disturb the roots of any aquatic plants if they are rooted in your aquarium. If the gravel bed becomes uneven, the water will tend to flow through the thin part exclusively, causing the area to become low in oxygen and unhealthy for aquatic plants.

In this article we have covered the various types of aquarium filters and their uses. Depending on the size of your fish tank, the species of fish, other organisms, temperature requirements, aesthetics and other factors, different types of filters will be suitable for you.

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