HOW AQUARIUM FILTER WORKS – Best filters, setup & uses

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The benefit of learning HOW AQUARIUM FILTER WORKS can never be overemphasized, Your fish tank filtration system is the key to keeping healthy water, and therefore healthy fish.

Having a good understanding of how aquarium filter works is one of the major milestones you need to achieve when you begin you aquarium hobby.

                                        Basic type of filtration found in aquariums

 Mechanical Filtration.

Mechanical filtration refers to any part of the filtration process that puts a physical barrier up to remove solid debris from the water. Usually, this can be found in the form of sponges, sieves, foams and matting, all capturing solid matter and particulate such as fish waste, surplus food, debris and anything else that turns your water murky.

Because mechanical filtration doesn’t do much to break down these big bits of aquarium rubbish, the mechanical stage your filter requires the most maintenance from you – clean the foams or matting from time to time with aquarium water, squeezing out the extra dirty water into a bucket. Even more periodically, you will need to replace your mechanical filter media, available from places like Swell UK.

Biological Filtration

The next stage of aquarium filtration is a little more advanced. Most filters feature a chamber containing biological filter media, often in the form of plastic balls with a high surface area to volume ratio. The water simply flows through the network of holes and gaps these balls create, but come into contact with cultures of nitrifying bacteria that colonise the balls (bio media).

This is where the filtration process really comes in:

Your fish create waste in the form of ammonia, the ammonia filled water goes into the biological filter and comes into contact with the nitrifying bacteria, which turns it from ammonia (a dangerous chemical) into Nitrites (still a little dangerous) and then into Nitrates (pretty harmless).

This is probably the most important part of fish keeping. Without adequate colonies of beneficial bacteria in your filter, your aquarium water would have a horrendously high ammonia content, burning your fish’s scales, inhibiting their breathing, feeding algae, and ruining your pH levels.

But while incredibly important, biological filtration takes time to become effective in a new fish tank. This is because the colonies of beneficial bacteria take a while to establish themselves, and to develop into quantities that can be effective.

This can lead to New Tank Syndrome where algae and poor water quality can be a factor. Consider the use of a filter start treatment, and fishless cycling to begin with.


An optional extra on smaller tanks, and considered essential by professional keepers of larger tanks, UV clarifiers are a fantastic extra augmentation for your aquarium filter system. These guys shine a powerful UV light into your aquarium water as it enters the filter, forcing algae particles to clump together so they can be caught by your filter media and broken down, curing most cases of Green Water, leaving you with crystal clear results.

Fluid Bed Reactors

This is where things get complicated, and unless you are trying to create something a bit special, most tanks won’t require a fluidised reactor, but we thought we best cover them a little anyway. Its best to think about aquarium reactors in the same way you think about a biological filter. They work in a similar way, but the difference is that the media is constantly on the move due to a current passing through the reactor, putting extra energy and oxygenation into the process to enhance the processes inside.

Best Filters For 29/30/40 Gallon Aquariums (REVIEW & GUIDE)

1. Polar Aurora Free Media 3-Stage External Canister Filter

Polar Aurora Free Media 3-Stage External Canister Filter

This canister filter is what we think would be the best if you want quality without breaking the bank as much.

Polar Aurora’s canister filters have always been popular among many fishkeepers out there.

It has a flow rate of 370 GPH so it is definitely rated for larger tanks such as those at 100 gallons.

It also has an adjustable spray bar so you can aim the nozzle anywhere you like. This would be useful for not blowing away your fish (especially the small ones). HOW AQUARIUM FILTER WORKS

The 3-stage filtering can be useful for thoroughly cleaning up your tank from debris such as fish ammonia. Its 9-watt UV sterilizer can help control the growth of algae and unnecessary bacteria (but not the beneficial ones!).

Things We Liked

  • Adjustable spray bar
  • High flow rate
  • 3-stage filtration system
  • UV sterilizer
  • Flexible media trays
  • Good customer service

Things We Didn’t Like

  • The flow cannot be adjusted

2. Fluval FX4High Performance Aquarium Canister Filter

Fluval FX4High Performance Aquarium Canister Filter

Yet another canister filter, this one may look like it’s rated for 250 gallons and above but it can also be used for those with a smaller tank size, such as 100 gallons.

It has a stackable set of media baskets so you can find it more effective than the layering system of other filters (which usually cause water bypass).

The filter has a strong rate of 700 GPH so it may be useful for larger aquariums with bigger fish. It also has a smart pump and a self-priming feature for convenience. HOW AQUARIUM FILTER WORKS

Every 12 hours, it also automatically evacuates trapped air so you don’t have to do this kind of thing manually. The tall design makes it compact and not obtrusive under most aquarium setups out there.

Things We Liked

  • Strong output
  • Self-priming feature
  • Automatic evacuation of trapped air
  • Stackable media baskets
  • Compact design
  • Comes with filter media ready to use

Things We Didn’t Like

  • Can be a bit pricey

3. Penn Plax Cascade Hang-on Power Filter Cartridges

Penn Plax Cascade Hang-on Power Filter Cartridges

Made for up to 300 GPH of flow rate, this filter cartridge set may work on your existing Penn Plax system.

It also has a carbon material that keeps its place inside the basket to eliminate water by-pass. The cartridge is ready to be used and sold in packs of 3.

The carbon material can be used for aquariums that have a terrible smell. It has no requirement for assembly so it can be a straightforward item for beginner fishkeepers. HOW AQUARIUM FILTER WORKS

You can use it just fine for both freshwater and saltwater tanks. Since it has two sides, it can be much more effective than store-bought filter cartridges.

Things We Liked

  • Activated carbon
  • The design prevents water by-pass
  • Works with most Penn Plax filters
  • Easy to install
  • Can remove odors
  • Can last up to 12 weeks

Things We Didn’t Like

  • Fits only Penn Plax Cascade filters

4. Fluval 406 External Canister Filter For Tanks Up To 100 Gallons – Crystal Clear Water

Fluval is a reputable brand in the world of aquarium pet lovers thanks to the quality of the aquarium filters they make. The Fluval 406 canister filter features a very large filtration capacity making it the best option to keep your 100 gallon fish tank clean for a long period.

The filter comes with four large media baskets for you to put any filter media into. The mechanical filtration stage is achieved through vertical large foam pads to capture more debris, prevent clogging and reduce maintenance. The design also makes it quick to maintain the mechanical media without having to remove media baskets.

Despite not being the quietest canister filter, the Fluval 406 operates quietly with its sound dampening impeller design. The impeller is also designed to last a long lifetime. It is one of the Best Filters For 29/30/40 Gallon Aquariums

Besides the good impeller, other parts of this filter are made of high-quality materials making the entire unit very durable. Some hobbyists reported that their Fluval 406 canister filters can last for over five years without any problems.

Pro Tip

What I love best about this model is its design for easy setup and maintenance. The filter features AquaStop valves designed to stop the flow of water without requiring you to disconnect the hoses, thus eliminating leaks and messes during maintenance.

It also features lift-lock clamps which rapidly and securely lock the lid in place for easily assembling the filter after cleaning. The instant-prime feature eliminates the need of manual siphoning to get the filter started.

5. AquaClear 110 Power Filter For Tanks Up To 110 Gallons – Very Quiet

If you are finding a versatile hang-on-back filter for your 100 gallon aquarium, the AquaClear 110 power filter is the best option. The filter boasts of its very large filter capacity that is 7 times as much as that of comparable models.

This means it can accommodate a huge amount of filter media for better filtration and impressive water quality. The large filter chamber also allows you to use any filter media you want.

It comes armed with a large foam pad, a bag of BioMax ceramic rings and an activated carbon bag. These filter materials are included in a patented re-filtration system (Cycle Guard) from Hagen Fluval that offers many helpful features. It is one of the Best Filters For 29/30/40 Gallon Aquariums

Thanks to the Cycle Guard, the flow rate of the filter can be adjusted but not affect its filtration efficiency. Moreover, this system also enhances the filtration efficiency by expanding the contact time between the filter media and the water.

Pro Tip

As with most hang-on aquarium filters, the AquaClear power filter is very easy and quick to install. You need no tools and experience to install it correctly as long as you can follow the instructions on the user manual


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