A Beginner’s Guide To Aquarium Filters

A Beginner’s Guide To Aquarium Filters

Chances are, you have probably seen aquariums all your life. Rectangular glass tanks with water sparkling in the light, with a bevy of fish in vivid colors flitting from one end to another, the bottom of the tank filled with rocks, pebbles, seaweed and algae look-alikes.

Yep, they’re everywhere - from the waiting area at your dentist’s to restaurants and hotel lobbies. Not to mention, you’ve also probably seen their bigger counterparts on weekend trips, either as a kid, or with your kids.

Whether big or small, nestled in a cosy corner of your house or proudly displayed along a hotel wall, there’s something fascinating about aquariums.


Isn’t it an absolute delight watching those fish move about in the water, and at one point or another you’ve probably tapped on the glass to move a fish that seemed to be enjoying a quiet nap behind a rock. So how exactly did aquariums come to be, and more importantly, what keeps them running?

What Are Aquariums?

From living rooms to hotel lobbies, aquariums have a special place in the world of decor. From basic ones that have a few goldfish, to some exquisite, custom-made ones that essentially bring the ocean into your home, aquariums are everything from a hobby to a subtle way of showing off fine taste and a love for all things fine.

At the core of every aquarium, however elaborate or simple, are a few common elements - a glass container, water, rocks, plants, fish, and the mechanism that keeps all these going in tandem - your aquarium filter, a.k.a its life support system.

Brief History

Today’s aquariums, as fascinating as they are, have a long history that goes back many centuries. From the Sumerians, who were the inhabitants of Mesopotamia, to the Egyptians, Romans and the Chinese, records of fish-breeding for food and entertainment date at least 4,500 years ago.

However, the honor of being the first to breed ornamental fish for decoration goes to the Japanese, who perfected the selective breeding of ornamental goldfish and carp. From the Orient, the practice of keeping goldfish in bowls reached the aristocrats of France, and later spread across Europe.

Historyof Aquariums

Although the practice of keeping goldfish in glass bowls was successful in England even in the 1700’s, aquariums as a common decor element only rose to fame after scientists, naturalists and botanists were able to decode and explain the relationship between oxygen, animals and plants, nearly a century later.

Technically, though, the credit of putting together the earliest version of the modern-day aquarium goes to two people- French-born naturalist, Jeanne Villepreux-Power and British naturalist, Philip Gosse.

While Villepreux-Power invented the first recognizable glass aquarium in 1832, it was Gosse’s work that the word aquarium came to be used to describe a container in which aquatic plants and animals could be held.

Before this, until the middle of the 19th century, the term ‘aquarium’ was used by botanists, specifically to describe a container used for growing aquatic plants only.

What Is The Purpose Of Aquarium Filters?

Irrespective of the kind of aquarium or the number or types of fish it hosts, its most crucial component is the aquarium filter.

You’ve probably seen it, in different forms - either a cylinder in a corner of the aquarium, or a box-like device suspended in a corner from top, constantly producing air bubbles - yes, that’s the aquarium filter, hard at work, keeping the water clean and giving the fish a healthy ecosystem to thrive in.

Your aquarium, apart from the fish, plants and little rocks and pebbles you put into it, also hosts a lot of other stuff, only some of which is visible to the naked eye. These substances, from fish excreta to chemicals like nitrates, can’t be left floating around, for reasons more than one.

Nitrate Test for Aquarium

For starters, some of these are downright harmful to the health of your fish, the others may end up damaging your aquarium. The best way to avoid both, is to get your aquarium a filtration system that cleans and refreshes the water inside it periodically.

Without an aquarium filter, you would be stuck with the task of manually changing the aquarium water every week, which is not only tedious and time-consuming for you but also traumatising for the fish, since they’ll have to be removed, and then put back (wouldn’t you rather have our fish swim happily while someone else takes care of the cleaning for you?).

So what exactly is an aquarium filter, and how does it work?

Cleaning Debris

The water in your fish tank or aquarium may be clean when you refill it, but just like the ocean, it becomes an ecosystem once you add living things like fish and plants to it. The fish in your aquarium are constantly excreting waste as they swim about, flushing out toxins from their own bodies, which, if left in the water to build up, can cause increased levels of ammonia, putting your fish at risk of ammonia poisoning from their own toxins.

Aquarium Filter Cleaning

Apart from this, the water in your aquarium also needs to be cleaned of other contaminants, such as leftover fish food, decaying organic matter, free-floating particles and dangerous chemicals.

In addition to affecting the health of your fish, these particles and substances will also give your aquarium a cloudy appearance, affecting its look and attractiveness. 

Getting Rid Of Ammonia And Nitrates

Ammonia, nitrites and nitrates are the chemical substances produced when organic waste such as fish excretions, plants or excess fish food start to decay and break down.

Just like in the ocean, all the living things in your aquarium are constantly letting out waste byproducts, and these undergo chemical reactions in the process of decomposing, which releases ammonia, nitrates and nitrites in the water.

Of these, high ammonia levels in the water are the most dangerous to your fish, as these can cause ammonia burns, and if not filtered regularly, eventually cause your fish to die as a result of ammonia poisoning.

The biological filtering process of water filters is what helps to break down ammonia into less harmful compounds like nitrites, which are then used by algae to grow, thereby keeping your tank clean and chemical-free.

Aerating The Water

Like all living things, fish need oxygen to live too. Most of the oxygen in your aquarium or fish tank makes its way downwards, from the surface of the water, and there are various factors that affect the oxygen levels in your tank.

The pH levels of water, its salinity, temperature, as well as the presence of any chemical additives to the water - all these can be responsible for making oxygen levels drop.

Here’s where a good aquarium filter will help, because it not only purifies and cleanses the water in your tank, it also aerates it by helping to produce and circulate oxygen in the water, and maintaining oxygen levels.

Optimum, stable oxygen levels are absolutely essential for a tank full of healthy fish, so an aquarium filter that does this well, is definitely an investment worth making!

Types Of Filtration

Aquarium filters need to work in three ways. Different types of impurities and toxins in the water have varying particle sizes, ranging from those visible to the naked eye, to ones that are only a few microns in size.

In addition, the removal of these different substances also differs - some can be physically filtered out, while others need to undergo chemical processes before they can be removed from the water.

Below are the three types of filtration that any aquarium filter must take care of, to leave your aquarium completely clean and free of impurities and toxic substances.

Mechanical Filtration

This is the process that will free your aquarium of large and small particles of organic waste, chemicals, or other impurities in the water. This works in the same way you might filter water through a cloth or a sponge filter - water flows continuously through an absorbent layer, and comes out cleaner and with less impurities.

Mechanical Filtration

Chemical Filtration

Chemical filtration is necessary to keep your tank free from chemical waste and toxic gases. While mechanical filtration works well to keep particles and visible impurities out, you need an aquarium filter with a chemical filtration system which helps by absorbing ammonia and other harmful chemicals from the water.

Chemical Filtration Systems

Most filters consist of a layer of media like activated carbon, which are scientifically proven to absorb toxic chemicals.

Biological Filtration

This is probably the most important kind of filtration you absolutely must have in place, if you want your aquarium to be healthy and clean. All the ammonia and nitrates you’ve heard of, are essentially produced by bacteria which break down organic matter found in your tank - a process known as the nitrogen cycle.

HealthyAquarium Bio Cycle

Biological filters consist of beneficial bacteria, which help convert ammonia into other substances which are not harmful for your fish, thereby ensuring that the nitrogen cycle of your aquarium tank works perfectly fine.

Types Of Aquarium Filters

Some Types of Aquariums

Power Or HOB Filters

These are the most commonly found filters for aquariums, known by both names - power filters as well as HOB filters, where HOB stands for “hang on back”. These filters are suspended into your aquarium tank by being hung on its backside.

Most power filters use all three types of filtration and are thus effective against all kinds of impurities in the water. The impure water from the tank is pulled into the filter by a pump, where it flows through a cartridge which contains some type of filter medium like activated carbon.

The mechanical filtration in power filters is really simple - as debris and free-floating particles come into contact with the filter, they get absorbed by the material or floss that the filter is made of. However, these particles tend to clog up the filter after some time, so make sure you rinse your filter and clean off the debris to prevent it from clogging.

Hob System Aquairum

The cartridge of power filters takes care of filtering out the chemicals. Some filters even come with special compartments or chambers where you can add particular additives in make the chemical absorption more effective.

In both cases, the frequency at which you need to replace the cartridge depends on the biological composition and volume of your tank water – if there is more waste, you will obviously need to replace your filter more frequently. 

Both, the absorbent and cartridge parts of power filters become home to bacteria that are helpful in absorbing or converting harmful gases like ammonia into other, milder substances. These bacteria grow with the time that your filter stays in the water, and become more effective with time.

Canister Filters

Canister filters are usually placed beneath the aquarium, and are pressurised units which carry out all three kinds of filtration. Some are available with a pump, while others in their modular form need an additional pump.

Once a canister aquarium filter is installed, it allows the water from the aquarium to flow down from the aquarium to the filter through a siphon. The canister aquarium filter has several layers, designed to help with different kinds of filtration.

First, water from the aquarium first passes through mechanical media such as floss or pads, where visible particles and impurities get removed. Next, it is forced through chemical media such as activated carbon, and finally, into the last chamber were biological filtration takes place, completing the nitrogen cycle before the water is returned to the aquarium through a spray mechanism.

Filter Carnister Aquarium

Since canister aquarium filters are pressurised, they force the water through a much finer material as compared to other kinds of filters, making sure that even the tiniest particles do not escape.

Canister aquarium filters will usually have a micron rating, which states the smallest size of the particle that they can effectively filter, allowing buyers to select one that best suits their aquarium.

In comparison, canister filters are not as effective as power filters in terms of biological filtration. Since they are not used in the tank, but under it and are pressurised in nature, there is little water-air exposure, which makes it difficult for beneficial bacteria to grow around canister filters.

Algae Scrubber

What’s the word “algae” doing in a list of filters, you might ask? While this one is easy to confuse with an actual scrubber/scraper used to clean algae off the surface of your aquarium, an algae scrubber is actually a filtration device that is particularly effective in keeping out the nitrates from your aquarium.

An algae scrubber is essentially a filtration system that uses light to grow algae in your tank - not the kind of algae that makes your tank messy, so there’s no need for you to worry.

Whether in the actual ocean, or in an aquarium, algae play a very important role in cleansing the water of the bad stuff, be it chemical pollutants, ammonia, carbon dioxide or other nitrous gases, and it is precisely this principle that algae scrubbers use in your aquarium, making use of a filtration system that is as close to nature as possible.

Alge Scruber in Aquarium

In an algae scrubber, water is forced to move rapidly over a rough surface that is highly illuminated. This causes algae to start growing in large amounts on the surface, which consume chemicals like nitrate, phosphate, nitrite, ammonia, ammonium and even metals such as copper from the water.

All of these chemicals are a hindrance to your aquarium - for one, they’re really harmful to your fish, and secondly, they’re also food for nuisance algae which will grow rapidly in your tank if these substances are left floating in the water.

In an algae scrubber the algae grow only inside the filter, as opposed to outside, in the aquarium water, and reduce both, the chemicals and nitrates present in the water, as well as, the growth of nuisance algae. Think of it as fighting bacteria with antibodies - algae to keep algae away. Once the algae in the scrubber filter have overgrown, they can be easily replaced.

You definitely can’t use an algae filter by itself - while it most certainly has excellent biological filtration, better than any of the other kinds of aquarium filters, you’re still going to need something to filter particulate matter as well as the chemicals that algae probably can’t absorb.

This being said, it is definitely a great way to include a filtration system that is organic, chemical-free and easy-to-maintain - once in, there’s nothing else you need to do.

Diatom Filters

Another type of filter which is similar to the algae scrubber, which makes use of a living thing is a diatomic filter. Diatoms are essentially single-celled organisms, which feed on silicates in the water. They use these silicates to create a protective silica cell wall around themselves, which is hydrous in nature.

When diatoms die, it is this shell that is left behind, which, due to its hydrous nature is full of pores. It is these pores, ranging in size from 3 to nearly 0.5 microns, that give diatomic filters their peculiar property of absorbing even the minutest of particles.

​The empty shells collect at the bottom of the water when diatoms die, eventually disintegrating and forming a sediment called either diatomite, or diatomaceous earth. This diatomaceous earth, when used in an aquarium filter, traps the tiniest particles, making it a great choice for mechanical filtration.

Diatom Filters Aquarium

​However, it becomes necessary to use another filter for the purposes of chemical and biological filtration, since diatomite is not as effective in these cases.

Also, a word of caution - be careful never to inhale diatomaceous clay while cleaning or replacing the filter - it is superfine, and could cause irritation in the respiratory tract, or worse, a possible infection if it is laden with impurities that have accumulated over time.

Internal Filters

There are many types of internal filters such as powered sponge filters, undergravel filters and canister filters. Of these, canister filters are fairly popular since they are cheap, easy to maintain, quiet and most importantly, they can’t be seen, which means they don’t distract from the charm of your aquarium.

Internal Filters Review

Essentially, internal filters are installed at the bottom of your aquarium, which makes removing or replacing them slightly inconvenient when compared to HOB or power filters.

This being said, you can install one and forget about having to replace it for a long time. Popular for being super powerful, internal canister filters are usually the top preference for buddying aquarists or those with small aquariums with a limited number of fish.

External Filters

External filters are only available as power filters, which are traditionally connected to the aquarium by an inlet pipe and an outlet pipe. External filters are bigger and more powerful than basic internal filters, and definitely more effective since they can be boosted for better filtration by  adding more media.

External Filters Aquarium

These work really well with bigger tanks, or tanks that have large fish. External filters are designed in a way that they can hold different kinds of mechanical, biological and chemical media, making them an all-in-one solution that caters to all the filtration needs of your tank.

As compared to canister filters which are fitted in the tank, at the bottom, external filters are fitted in a separate cabinet under the tank, which makes them discreet and quiet but also means additional installation time and space, and can be more expensive as compared to basic internal filters too.

Maintenance And Cleaning

Depending on what kind of aquarium filter you choose, you should find it easy or difficult to clean and maintain it, but all types of filters definitely need maintenance of some kind.

The last thing you want is a filter that hasn’t been cleaned in weeks, and is doing exactly the opposite of what it should be doing - polluting your aquarium with all the toxins and dirt that has accumulated with time but has no other place to go.

Ideally, you should clean your aquarium filter once in every four weeks and if you have an algae filter, it needs to be cleaned as soon as the algae has grown too much.

If you are using a power filter in a saltwater aquarium, it will need to be cleaned more frequently, as the salt in the water can form a crust on the filter’s surface, hindering its ability to filter the water effectively.

The easiest way to clean an aquarium filter is to rinse off all the visible debris, and then to gently wash it with water, using warm water in the case of a slimy build-up on the surface.

Make sure you thoroughly wash any other cleaning substance you use - you don’t want to end up adding more pollutants to your aquarium instead of removing them.

Another important thing to know about power filters - if you are replacing your filter cartridge, you will end up losing the beneficial bacteria that have grown on it over time.

A good tip is to place the new cartridge in either in the aquarium or the filter to allow the beneficial bacteria to grow before removing the old one, which ensures that the nitrogen cycle of your tank does not get disrupted.

This should have cleared any doubts in your head about why you need an aquarium filter, or what types of aquarium filters are available. Now that you’re clear on the basics of aquarium filters, the next step is pretty obvious - go back, take a good look at your aquarium. What is the kind of water you use in there? How many fish do you have?

Most importantly, what are the biggest issues you’re facing in your aquarium - is it an excessive buildup of ammonia and nitrates, or unchecked algae growth?

Only you’ll be able to tell, so before you set off to buy your aquarium its next filter, make sure you’ve given all of this a good thought. After all, you want to buy an aquarium filter that gives your fish the healthiest aquarium they can thrive in, don’t you?

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