Fluval is a very well-respected brand known for its durable and brilliantly designed products. The Fluval C4 Power Filter is no exception. It is designed for aquariums between 40 and 70 gallons, and is widely regarded as one of, if not the best, power filter on the market. It is no surprise that it comes in at number one on our list of the best HOB filters.

Aquarium enthusiasts often face a challenge when it comes to maintaining a healthy and thriving aquatic environment. Water quality is crucial, and a good filtration system is essential to achieving this. The Fluval C4 filter is a powerful and reliable aquarium filter that can help maintain a healthy aquatic environment in both freshwater and saltwater aquariums.

The Fluval C4 filter has a sleek and compact design that can fit into most aquarium setups. Its dimensions of 7.5 inches by 9 inches by 8 inches make it suitable for aquariums up to 70 gallons in size. It is easy to install, with a simple clip-on design that allows for easy maintenance and cleaning.

But is it worthy of its reputation?

Fluval C4 Power Filter, Fish Tank Filter for Aquariums up to 70 Gal.
  • 5-stage clip-on power filter designed for freshwater and saltwater aquariums between 40 and 70 gallons
  • Two mechanical stages trap large and fine debris, foams easily slide out for quick cleaning
  • Chemical stage with activated carbon effectively removes toxins
  • Biological stage features Bio-Screen pad, blocks debris and provides massive surface area for beneficial biological activity
  • Biological Trickle Chamber super charged for fast and efficient nitrification when loaded with Fluval C-Nodes


Fluval C4 Power Filter Review

This article will review the Fluval C4 Power Filter in depth and highlight all of the great features which have resulted in this clip on filter being widely regarded as the best power filter on the market today.

One of the key features of the Fluval C4 filter is its advanced mechanical filtration system. The filter uses a patented five-stage filtration process that includes a mechanical pre-filter sponge, a bio-screen, and a clog-proof intake strainer. The pre-filter sponge removes large debris and waste particles from the water, while the bio-screen and intake strainer work together to prevent clogs and maintain optimal water flow.

In addition to its mechanical filtration capabilities, the Fluval C4 filter also offers advanced chemical filtration. It includes a customizable chemical filter insert that allows hobbyists to choose from a variety of filtration media, including activated carbon, ammonia remover, and nitrate remover. This ensures that the aquarium water is free from harmful toxins and contaminants.

The Fluval C4 filter also features an advanced biological filtration system. It uses a patented BioMax biological filter insert that provides a large surface area for beneficial bacteria to grow and thrive. These bacteria help break down waste and toxins in the water, promoting a healthy and thriving aquarium environment.

The Fluval C4 filter is also designed for quiet and efficient operation. It uses a powerful and energy-efficient motor that operates at a low noise level, ensuring that the filter does not disrupt the peaceful environment of the aquarium. Additionally, the filter includes a flow control feature that allows hobbyists to adjust the water flow rate to suit the needs of their aquarium and aquatic creatures.

Maintenance and cleaning of the Fluval C4 filter is also easy and straightforward. The filter includes a self-priming feature that eliminates the need for manual siphoning or pumping to start the filter. The filter media is also easy to access and change, thanks to the filter’s easy-to-open cover.

In comparison to other aquarium filters, the Fluval C4 stands out due to its advanced filtration technology. For example, a power filter typically only offers mechanical and biological filtration, while the Fluval C4 filter provides all three types of filtration. This multi-stage filtration process ensures that the aquarium water is free from debris, toxins, and contaminants, promoting the health and well-being of the aquarium inhabitants.

Another benefit of the Fluval C4 filter is its ease of use. The filter is easy to install and maintain, thanks to its clip-on design and self-priming feature. This means that hobbyists can spend more time enjoying their aquariums and less time maintaining them.

Finally, the Fluval C4 filter is also cost-effective in the long run. While it may be more expensive initially compared to other filters, the filter media lasts longer and is more efficient, reducing the need for frequent replacement. The filter also has a longer lifespan compared to other filters, further reducing costs in the long term.

Capacity and output

The great thing about Fluval’s C series Power Filters is the relatively large capacity and output. 

The Fluval C4 Power Filter is designed for aquariums of between 40 and 70 gallons. It has an output of 264 gallons per hour. This is very impressive for a power filter, as they are normally designed for much smaller aquariums than this.

However if you do have a smaller tank, you don’t need to go to a different filter. The Fluval C series power filters also come in two different sized models as well. 

The Fluval C2 Power Filter is designed for tanks of between 10 and 30 gallons, with an output of 119 GPH; while the Fluval C3 Power Filter is designed for tanks of between 20 and 50 gallons and has an output of 153 GPH.

5 Stage Filtration

The unique thing about the Fluval C4 Power Filter is the integration of 5 stage filtration. Power filters are normally lucky if they have all three of mechanical, chemical, and biological filtration. 

But with the Fluval C series power filter you get the filtration power of a canister filter with the ease of a hang on back clip on filter. Read our article canister filter vs power filter for more information on the differences.

The five stages of filtration include two mechanical stages, one chemical stage, and two biological stages. All the filter media is included, which is ideal.

The two mechanical filtration stages are a porous foam which captures large particles and a dense poly layer which captures the finer particulates. 

At the third step comes the chemical filtration media; activated carbon absorbs any unwanted odors, impurities, and discoloration. An additional design feature is that the chemical basket is very versatile. A carbon sachet is initially given with the C4 Power Filter but it can be replaced with any bagged media. So you can choose a chemical media of your own choosing if you so desire. 

Then comes the two biological filtration media. Firstly the bio-screen blocks any remaining debris from entering the biological stages of the filter. It also contains a micro weave which provides an extremely large surface area for bacterial colonization. Finally comes the biological trickle chamber with C-nodes. These are enriched with oxygen which enable them to swiftly reduce the levels of ammonia and nitrate in the water.

Fluval C4 Power Filter, Fish Tank Filter for Aquariums up to 70 Gal.

The foam pads will need changing quite regularly, about every two months. This is more regularly than other filter pads, but it says something about how effectively they catch dirt and debris!

Refiltration control system

This is a patented feature unique to the Fluval C Series Power Filter. There is a switch situated on the shell of the filter which allows for slower release of water from the filter as well as increasing the water filtration dwell time in the filter.

This is a brilliant feature, as many fish and plant species are very sensitive to strong currents of water. Having a slower more controlled release of water will enable these plants and fish to feel fully comfortable in your tank. 

The increased dwell time of the water in the filter means that the water has increased exposure to the filter media. Essentially this means the water that comes out of the filter is cleaner and more purified.

The telescope intake tube allows for control at what depth the water is taken into the filter, and so adapts to a number of water parameters.

Independent filtration stage management

Being able to independently manage the different filtration stages is a very good design feature. It means that you will be able to make changes to the different media at different times while maintaining continuous biological activity. 

This is great as when you change the filter media biological filtration will continue so you won’t have spikes and troughs in the quality of your aquarium water. 

Cleaning indicator

You won’t have to worry about when to clean this HOB aquarium power filter; there is a very handy cleaning indicator which pops up and tells you when it is due.

The cleaning indicator shows when the two mechanical media pads need cleaning or replacing.

Easy maintenance – Quick release media cartridges

Another great plus point is that cleaning and maintenance is extremely easy with the Fluval C4 Power Filter. 

With quick release media cartridges you can get each type of media out individually to clean or replace whichever piece needs it. 

The mechanical foam media slips out very easily for easy rinsing and changing. So too does the chemical media, being very easy to remove with a draw tab which easily removes the chemical basket from the filter.

You can also read our article on how to clean and maintain an aquarium filter.

The slightly annoying thing is that there are quite a few places in the body of the filter, especially around the impeller, that can make cleaning a little painstaking. This doesn’t take anything away from the effectiveness of the filter itself. But using a brush (an old toothbrush works wonders!) is a good idea.

Fluval C4 Power Filter, Fish Tank Filter for Aquariums up to 70 Gal.

Small footprint

Canister filters can be housed underneath or next to your aquarium, drawing in and returning the filtered water to the tank via tubing. Power filters don’t have this luxury, and instead hang or clip onto the tank itself. 

Due to this the best power filters have a small footprint so they take up as little space as possible. 

This is true of the Fluval C4 Power Filter. It measures 9″ in length, 6.5″ in width, and 8.5″ in height. This relatively small size means that you shouldn’t have any issues with having the space to attach this power filter to your tank. 

The Fluval C2 Power Filter measures 7 x 5 x 6″ while the Fluval C3 Power Filter measures 7 x 5 x 7″.


The installation is very quick and simple. There’s no playing around, you simply put all the filter media into their compartments and you are good to go. 

Have a watch of the following video by Fluval themselves of an unboxing of the C Series Power Filters. The video includes how to properly setup the filter medias and everything else you need to know.


As a final call, the Fluval C4 Power Filter really is arguably the best power filter money can buy at the moment. Overall, the Fluval C4 filter is a reliable and efficient choice for maintaining a healthy and thriving aquatic environment. Its advanced filtration technology, ease of use, and cost-effectiveness make it a popular choice among hobbyists looking for a reliable and effective filtration system for their aquariums.

With five stage filtration, a filtration control system, independent filtration stage management, and easy maintenance, there are great features which really make this filter stand out from the rest. In summary, the Fluval C4 filter is a powerful and efficient aquarium filter that offers advanced mechanical, chemical, and biological filtration capabilities. Its compact and sleek design, quiet operation, and easy maintenance make it a popular choice among hobbyists looking for a reliable and effective filtration system for their aquariums.

If you have a tank of between 40 and 70 gallons then this power filter will be a great choice for you. Don’t forget that if you have a smaller tank then you can always go for the Fluval C2 Power Filter or the Fluval C3 Power Filter.

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