Best Aquarium Filter. 2021 Top Picks Reviews and Guide (FAQ)

Getting the filtration right in your tank and picking the best aquarium filter for your set up is one of the most important elements of successful fish keeping.
The water in your tank is literally the air that your fish breathe.
As aquarist, it’s your responsibility to make sure that the water in your aquarium is sparkling clean at all times, so if you are looking for the best fish tank filter to use, you have come to the right place.
In this article we’ll cover everything you need to know about filtering the water in your aquarium, from biological to chemical to mechanical methods.
We’ll also review the five best aquarium filter types to buy on the market so that you can determine which filter is the best fit for you.

The Hydor Professional filter is easy to set up and simple to use.
It has an easy priming system that will make starting it up a dream, despite the instruction manual for assembly, which is mainly pictures without much useful accompanying text.
The filter is mounted on the outside of the aquarium (hence “external”) and has been designed to make the best use of space.
It also has an expandable spray bar that comes in four different sections, meaning that you can customise the water flow as well as choose the placement and length that will work best for your tank size.
The Hydor Professional filter has a rectangular design that fits more filter media than most (you’ll get between 3-5 filter media trays, depending on the model), making the higher capacity a plus for bigger aquariums.
A special ‘no bypass’ design means that water always flows through the filtration media.

The filter has been fitted with a highly efficient motor and excellent soundproofing, so it operates very quietly.
The sleek design also minimises leaks, but be careful when disconnecting the valves to clean the filter as this is when you might run into some leaks.
As Hydor is a relatively new entrant to the filter market, you might find it tricky to find replacement parts if something goes wrong down the track.
However, their website is useful and customer service is good.
Some users have reported that they’ve been able to find replacement component parts at big-box hardware or plumbing stores without any issues.

The design of undergravel filters means they need to be tough to withstand the weight of gravel, water and ornaments bearing down on them constantly.
The Lees Premium Undergravel Filter uses a multi-level design made from toughened plastic plates that can support heavy gravel loads, as well as live rock and hefty decorative elements, even in tanks up to 135 gallons.
The combination of structural strength combined with good resistance to cracking and splitting make this filter a favourite with saltwater aquarists.
The filter has a gentle slope towards the front of the tank, so it helps your substrate look good in the water and will keep your plants and decorations firmly in place.
The Lees Premium Undergravel Filter comes in a range of sizes to suit your tank:

Every model comes with moulded gravel guards that help stop gravel falling into the undergravel uplift tube, as well as 2 fish-saver elbows to help protect your finned friends.
You’ll also receive 2 Discard-A-Stones to help keep your aquarium water oxygenated, and at least 2 premium carbon cartridges to aid in filtering out dissolved chemicals and impurities from the water.
For best performance, these carbon cartridges and Discar-A-Stones should be replaced every 2-3 weeks.

Using this filter isn’t a set-and-forget option though. You’ll still need to do regular water changes, and when you’re using an undergravel filter, you will also need to regularly vacuum or siphon your gravel. This will help to remove additional dirt and particles that cling onto the sides of the gravel, and it will keep your aquarium in good condition.

For additional effectiveness, you can use an additional power filter with the Lees Premium Undergravel Filter. It has 3-4 ports in the set-up. But if you don’t, then just cover them up with the caps that are included in the set-up package.

These filters are renowned for living long lives without needing any maintenance, so they’re hardy and durable to boot.
The big design feature of the AquaClear filter is a “natural and silent waterfall” that filters the aquarium water from the bottom of the filter upwards, along with a specially patented flow control feature that means you can customize the performance of the filter as you like.
It also has a gigantic media basket that you can pack full of your favourite media, though it does come fully equipped with a range of products from the AquaClear range, including AquaClear Foam, Activated Carbon, Cycle Guard and BioMax.
You can supplement these components with others from the range that have been designed for use with the filter, such as Zeo-Carb and Ammonia Remover, or swap out one type and add another, such as a sponge.
As with all filters that use a triple-punch filtration method, there will be some expense in the upkeep of this filter, as you’ll need to replace the disposable elements from time to time.
It’s recommended that you replace the activated carbon insert every month, the foam filter insert every two months, and the BioMax insert every three months.
If you have a tank that’s larger than 30 gallons, you can consider the other sizes in this model:

Some users have noticed that the instructions for this model could be more clear.
But don’t worry about this too much. YouTube is your friend here and there are plenty of installation videos that can show you how to set the filter up properly.

More immediately, once the filter is set up correctly there’s also a tendency for debris to get trapped in the propeller box, so you’ll need to keep an eye on it and clean it out regularly.
The AquaClear 30 Power Filter comes with a two-year warranty from the manufacturer.

The Aqueon ProFlex Sump filter is a versatile beast, with a three-chambered filtration system that you can customize to set up as a refugium option, wet/dry option or Berlin style sump.
It has an adjustable spill over wall to help set the water height in the second chamber. You can then adjust the second chamber to create a refugium style system, or use an optional BioMedia pack to convert the sump into a wet/dry filter. The wall can also be lowered to allow a constant volume level for use as a protein skimmer chamber for a Berlin Method set up.
The third chamber is designed to hold a submersible circulation pump to return the water back to the aquarium.

This option is a good idea for reef aquariums, where a large protein skimmer is important. The sump chambers are roomy enough to put a large protein skimmer here and ensure a constant water level.


You can choose to turn the ProFlex into a traditional wet/dry trick filter by using the BioMedia Accessory pack (sold separately). Traditional wet/dry filters are great for use in freshwater and fish-only saltwater applications to provide advanced biological filtration for a heavy fish load.

The accessory pack includes filter media and a filter tray, a trickle-down grid, and bioballs.
As water enters the ProFlex body, it flows through a bubble diffuser chamber that has been specially designed to significantly reduce noise by expelling the bubbles. After the water has been through this chamber, it enters two filter socks at 200 microns in order to catch and retain large particulate matter.
These filter socks will clog easily if you don’t keep an eye on them, so be sure to clean them regularly to ensure a longer life for the sock and a cleaner environment for your fish. It’s worth considering a second set of socks so that while one is being cleaned and drying, the other set is already in your tank and doing its job.
The Aqueon ProFlex Sump filter comes in a range of different sizes to fit your tank:

You’ll need to separately purchase an appropriate siphon overflow box, return line and a pump to run this filter, however, as the Aqueon ProFlex Sump filter doesn’t include those components in the pack.

Of course, it’s designed to pair perfectly with the Aqueon Submersible Utility Pump though.
Make sure you assemble the unit properly, or you might find it makes some additional noise and vibration.
This filter has a simple, streamlined design and the usual Aqueon lifetime warranty against leaks. Watch out for salt creep and ensure you keep it clean.

The “Smart Pump Technology” in this filter is pretty advanced, and it uses an electronic circuit board that helps to keep everything working in perfect balance. It constantly monitors the pump and measures impeller speed and force. This system also manages the filter’s self-starting feature and automatically releases trapped air from the filtration system on a 12-hour cycle.

It sounds complex, but in fact the filter is easy to set up. All you need to do is prime it with water and plug it in. And it comes with a handy in-built feature to remind you about your maintenance obligations! There are two indicator dials on the top of the unit to help you remember when you last did a water change (on the left dial) and when you changed the filter media (on the right dial).

Speaking of filter media, one great feature of this filter are its removable media baskets. These baskets form the centrepiece of the multi-stage filtration system. You can add or remove filtering material easily, and the baskets are precision-engineered so that there is no water bypass.

You can stack these baskets in the way you like. Every basket is lined with a foam insert as a method of mechanical pre-filtering, and instant release T-handles make your cleaning routine simpler because you can get the baskets in and out, quickly and easily.

And by the way, the filter media comes as part of the package – so there’s no need to buy any additional methods or materials unless you’d like to use something different than what’s provided.

Another great feature is the water change feature. When you’re running a tank of up to 400 gallons, that’s a lot of buckets to carry when you need to do a water change.

The Fluval Canister Filter FX6 saves you the sweat because it has an output attachment where you can just attach the hose and the FX6 Smart Pump Technology takes care of the rest.

This isn’t a standard inclusion, so you will need to purchase the hose kit separately, but think of how much easier this could make your regular cleaning routine.

As one of the bigger names in filtration systems, Fluval also has a range of on-brand accessories, add-ons and filter media that you can choose from to help your system run smoothly and efficiently.
If you are running high capacity aquarium systems, we know the choice of the filter is critical. Here is why we have reviewed aquarium filter for large tanks as well in more details in a separate article.

The Fluval Canister Filter FX6 comes with a three-year manufacturer’s warranty. It’s more expensive than other filters on the market, but it’s a reliable workhorse for a big tank and definitely worth considering the investment.

When it comes to filtration in your aquarium set up, rest assured – this is NOT an optional extra.
After the water and the fish, filtration and getting the best aquarium filter for your setup is the next most essential element of your successful fish keeping pastime.

Just like people, fish release by-products every minute of the day (and night) just by living their everyday lives.

They breathe water through their gills, and in the process, they expel salts and ammonium.
They eat food, and after they’ve digested it, they excrete the waste into the water, which includes nitrates and other harmful chemicals.

Unlike people though, the fish have to keep ‘breathing’ that same water.

An aquarium is a contained environment.
What goes in the tank is going to stay in the tank unless there is some kind of mechanism to clean it up.

If the levels of ammonium, nitrates and other toxic chemicals build up to dangerous levels inside their aquarium, it can cause your fish to sicken and even die.

It doesn’t take long for this to happen, and the water might not even be visibly dirty to you.
You could leave the house in the morning with fish that seem fine, and come home to your worst nightmare.

Of course, there are variables involved when determining what a dangerous level of these toxins is.
For example, it will be different for a coldwater tank versus a tropical one.
A big tank with a few small fish will last longer than a small tank with lots of fish.
A planted tank might last longer than one without plants.
And there are many other elements that all affect the situation.

But even with all the variables, there is one key fact that always stays the same.
If fish swim in dirty water for too long, it will poison them.
To solve this problem, you need a filter.

The filter in your fishtank performs a range of functions, all of which help to keep the water sparkling clean and healthy for your pets.

A filter removes particulate waste and decaying organic matter from the water. This includes excess food or rotting food, poop solids, dust particles that have fallen in from the air, bits of rotting plant, and other things.

A filter will also remove the harmful chemicals that build up from your fish’s natural excretory processes – ammonium, nitrates and other toxins. If these toxins aren’t removed, they can quickly reach a high concentration in the water and poison your fish fast.

There are three different methods of aquarium filtration: biological, chemical and mechanical.

Every fish tank uses biological filtration at a bare minimum. Fishtanks are little ecosystems, and to stay in balance they need a healthy colony of “good” microbes and microfauna that help to filter the water and keep it clean.

Then, other filtration methods can be added to increase the filtration potential or to deal with a heavier load than a simple biological method can handle.

These additional methods are chemical filtration and mechanical filtration.

Some commercial filters will use all three methods at once, in order to provide the best outcome – which is a safe and clean environment for your fish.

Biological filtration uses living organisms to help your fish tank naturally break down and deal with the waste produced by your fish, plants and other aquatic species.
Basic biological filters have three different elements:

Substrate actually works as the most important element of a biological filter system, as it provides a large surface area for micro-organisms to grow and flourish.

It’s important that you “season” a substrate before you introduce any fish to your tank, as it takes 1-2 weeks for healthy bacteria to begin growing naturally on gravel or sand. Ensure that your tank is set up with substrate and plants for this period before you add any fish. After the 2 weeks, add just a few - 2 or 3 is a good number - and leave them to settle in before you add any friends. This will give the bacterial colonies time to grow inside your tank without dying in an onslaught of fish waste!

Because gravel is so important in biological filtration, it’s also important to clean it regularly when you’re doing water changes. Use a gravel vacuum to suck up any larger bits of food, waste or other organic matter that is too big to be handled naturally. Never clean your gravel in hot water or you’ll kill all those little microbes you’ve worked so patiently to establish.

Plants are also a very important part of your bio-filtration system. There are many potted, rooted or free-floating plants that can help do this job of keeping the water clean. Always be sure to match your plants to the fish that you’re keeping, as you can’t just choose something at random and hope it will work.

You can also use invertebrates to help keep your tank clean, along with live rock or live sand, though these latter two are for saltwater tanks only.

If you’ve got a freshwater tank, then you can also boost the biological filtration by adding special invertebrates such as crustaceans and snails – they’ll help filter the water too. Of course, these invertebrates need their own kind of special care, so ensure you’ve read up on the requirements and make sure you’re prepared to look after them as kindly as you look after your fish.

If you’re running a saltwater tank, then you might also consider using a refugium.
Establishing a refugium essentially involves creating a special “safe zone” in a large sump-type filter, or in a smaller and separate (but connected) aquarium, which basically works as a protected habitat for microfauna.
Live rock, live sand, and other types of plants and algae in this safe zone can help control excess nutrients that could otherwise interfere with the healthy growth of corals in the main body of the tank.

Chemical filtration works by using carbon or chemical resins or other adsorbent materials to clean up the dissolved particulates in your aquarium.
You heard right – adsorbent, not absorbent.

Activated carbon is full of millions of tiny pores or holes, that act as little “pockets” for all the stuff that’s dissolved inside your tank.
These pockets collect all the dirt and muck until they’re full, whereupon the carbon turns into a biological filter, because bacteria will land on the surface and grow as they eat the rubbish.
That’s when it’s time to replace it.

Chemical filtration can remove other chemicals such as copper and chlorine, as well as dissolved proteins and carbohydrates that are found in fish food and waste.

You should be aware that carbon can absorb plenty of other things, such as any medication you might be using in your tank.
Pay particular attention to antibiotics.

If you’re treating your fish and your tank water, take the carbon out first and don’t return it to your aquarium until after the treatment period is finishes.

When it comes to other chemical filtration options, resins aren’t as popular as carbon, but they will still do the job.

They work by attracting a special molecule such as ammonia and nitrate.
They’ll strengthen the efficacy of carbon though, so it can be a good idea to use them together.

Mechanical filtration works by straining the aquarium water through a “medium” to physically trap the debris and particulate matter that’s floating around in your aquarium.
This might be a foam pad or sponge, floss, or some other kind of material that’s placed inside the filter to catch the muck as it passes over or through.

There are two key elements in making sure your mechanical filter is working to its best potential: flow rate and filter media.

Your mechanical filter is a little bit like Goldilocks.
It needs a water flow rate that’s just right – not too fast and not too slow.
Mechanical filters tend to come with their flow rates preset, but you can often change these manually.
Be aware of the variables that will impact how fast you want the water to flow through the filter in order for it to work effectively and keep your fish happy and healthy.
For example, you might want to slow the flow rate down if you’re keeping bettas.

Filter media is the other key element.
Sponges, pads and blocks for mechanical filters (usually canister filters and power filters) can be purchased in an infinite range of shapes, sizes and densities.
You need to choose one that has the right pore size for your aquarium with all of its variables.

A pore size that’s too small will clog up very quickly and you’ll need to clean it more often than you’d like.
A pore size that’s too large won’t trap the muck that it needs to.
Make sure to remove your mechanical filter on a regular basis to clean it and replace the filter media when necessary.

If you don’t do this, the trapped material will build up and rot back into your aquarium.
This will kill the healthy microbes in your media and you’ll be back to square one.

There are a number of different kinds of mechanical filter that you can choose for your tank:

There are many different variables you need to consider when you’re choosing the right aquarium filter for your tank.
These include tank size, filtration technology, whether you’re running a coldwater or a tropical tank, freshwater or saltwater/reef, your fish load, the strength of the filter, the lighting on your tank and many other things.
However, the top three things that should determine your choice of filter are:

When it comes to choosing a filter, this is an area where you don’t want to scrimp and save. Filtration is the most essential part of your fishkeeping equation, and it is often better to find the best filter and invest in it rather than trying to get filtration right “on the cheap”.

There are a number of trusted and reputable brands in the filtration world, including Eheim, Aqueon, Aquaclear, Fluval, Hydor, Penn Pax and others. These companies have been making filters and/or fishkeeping component parts for many years, and they’re the experts.

How you clean your filter will depend on what type of filter you’re using – there are different methods for cleaning biological, mechanical and chemical filters; as well as the mechanisms they’re fitted in – whether that’s undergravel, HOB, canister, power or other kinds of filters.
Your filter will come with an instruction manual, so make sure you read the recommendation from the manufacturer.
You can also check reference videos on YouTube for all of the different kinds of filters.
You should always rinse or clean your filters and filter media in water from your fishtank, so that you’re keeping the beneficial bacteria that have colonised those materials.
Never clean a filter under the tap!
You’ll kill off all the healthy microbes that are helping to keep your fish tank clean and your fish in good health.
If you have a canister filter check out our article for a more detailed answer on cleaning a canister filter.

Clean a sponge or foam pad by swishing it around in water that you take out from your aquarium – you’ll only need one or two cups.
First, unplug your filter.
Then remove the pad or sponge. Use your hands to squeeze the sponge or pad firmly in the aquarium water that you’ve removed – this pushes the water through it and the velocity will help to remove nasties from inside, where you can’t reach.
Keep doing this until the water runs clear when you squeeze.
Give the casing and tubes of your filter a scrub in the water too.
Wash off all the gunk from the pad or sponge with your hands and then replace the item inside your filter (and remember to switch it back on!)

Biological filters such as plants and moss balls don’t need to be cleaned very often at all.
If you think you do need to clean a moss ball, be gentle and make sure you do it in water from the tank while you’re doing a partial water change.
Gravel will need to be vacuumed every 1-2 weeks to help catch particles and other matter that has gotten trapped around it.

Chemical filters don’t need to be cleaned.
Instead, they need to be changed regularly, for example around every 3-4 weeks.
Try to get into the habit of doing this every month when you’re doing a water change.
If you have a heavy fish load or other variables that affect water quality, you might need to replace the inserts more often, or whenever the water gets too cloudy.

The quick answer is: clean your filter when it’s dirty!

But most importantly, make sure you’ve left at least a week between any other kind of change in the tank – a water change or other any other change in the environment.
Fish don’t like stress (who does?) and cleaning your filter too soon after another disturbance isn’t kind on your pets.
Cleaning time will also depend on other variables in your tank.
Are you running a heavy fish load?
What’s your tank capacity?
Are your fish or plants recovering from any pests or diseases?
Is it a coldwater tank or a tropical one? What kind of lights are you running?
As a responsible fish owner, you must keep an eye on your filtration system with all these variables in mind.
Common sense tells you that a small filter in a big tank will need cleaning more often than a big filter in a small tank, but there’s a lot more that goes into it.
As a general rule of thumb however, you should be prepared to clean your filter at least every two weeks.
Filter socks might need to be cleaned more often, depending on the amount of particulate matter they’re catching in your tank.
You will also need to completely replace activated carbon inserts every month, foam filter inserts every two months, and if you have a BioMax ceramic ring as well, it will need replacement every three months.

You can confidently use an aquarium filter in a planted tank – in fact, you can choose from a range of filter options.
While the plants are already providing a biological filter function, it’s unlikely that the plants themselves can perform the level of filtration that’s necessary.
So it is a good idea to supplement this with mechanical filtration in order to remove particles from the water.
However, you also want a filter that isn’t going to create a strong current in the water.
In general, start with a filter that can move 7 to 10 times the amount of water in your tank. 
This will help keep your plants swaying gently but not too much.
Make sure the flow comes from the back of your tank, through to the front.
This will help distribute the water and CO2 your plants need across the whole aquarium.
HOB, canister filters, internal filters and wet/dry filters can all be good options for your planted tank.
Undergravel filters don’t tend to be suitable unless you only have small plants that don’t root deeply – otherwise they can wrap their roots around the filter system grid.

A small tank of less than 10 gallons without a filter is possible – but it’s a lot more work and it’s something that only experienced fish keepers should consider. Which is the opposite of what usually happens!
Choose a filter that is small enough for your fishbowl or tiny tank. There are mini filter options available that will help to keep your fish healthy – ammonia and nitrate levels can spike quickly in a small tank. With a small tank there’s less room for toxic chemicals and your fish can die quickly.
At the minimum, choose a biological filtration option in the form of suitable plants, or ornaments such as marimo moss balls. These moss balls aren’t just cute – they’re live plants that absorb nitrates from your tank, including phosphate and ammonia. And as they’re a living plant, they help to oxygenate the water.
If you’re running a small tank of 5 gallons, having some of these can be a great option to help keep the water fresh without needing to use a mechanical or power filter – though you can also consider those too as there are some good options on the market.

So there you have it – the definitive guide to filtration in your tank.
No matter what kind of tank you’re running – freshwater or saltwater, coldwater or tropical, big tank or small – there is a filter out there that’s right for you.
When you find it (using our handy guide as a reference, of course!), you’ll be on your way to giving your fish a happy, healthy life in a tank that’s full of clean, sparkling water.