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Fluval FX6 Review: The Complete Guide

Canister filters are typically what intermediate and advanced aquarists prefer over the hang on the back power filters. They provide more water turnover, are easier to regulate, and have space for specialty filter media.

However, not all canister filters are created equally. Right now, the hottest product on the aquarium market is the Fluval FX6, a high-end canister filter designed to meet the needs of intermediate and advanced aquarists. Let’s take a look at what makes this filter so special!

Fluval FX6 Specifications

  • Circulation: 563 US Gal/h
  • Mechanical Filtration Area:5 in2
  • Biological Volume:5 US Gal
  • Aquarium Rating: Up to 400 Gallons
  • Dimensions:75 x 15.75 x 20.8″
  • Warranty: 3 years
Fluval FX6 High Performance Aquarium Filter, Canister Filter for Aquariums up to...
  • Multi-stage filter pumps out 925 US Gal (3,500 L)...
  • Self-starting – just add water, plug in and...
  • Easy water changes eliminate need to lift heavy...

Benefits of the Fluval FX6 Canister Filter

Here are some of thee main benefits for the Fluval FX6 Canister Filter:

Incredibly High Water Turnover

The pump output is rated at 925 gallons per hour, but the filter turns over roughly 523 GPH. This means the Fluval FX6 works for aquariums of up to 400 gallons but can also be used in aquariums as small as 55 gallons, depending on your inhabitants.

For a small fish community the FX6 would be absolute overkill. However for reptile and amphibian setups the FX6 would be perfect because these animals create copious amounts of waste and can foul an aquarium in just a few days.

Despite the increase in capacity and output relative to the previous models the FX6 uses 10% less power. This is made possible not only by a more advanced motor design but a smart microchip monitoring system that continually tracks water flow, air contained in the system, and power usage. Each factor is constantly modulated to best regulate the filter’s output!

The high flow of the Fluval FX6 also allows you to make good use of the current it creates. At the minimum, the current maintains proper water turnover which improves oxygenation and evenly distributes heat. In large aquariums, using a weak filter that creates little current can lead to stagnant or cold zones.

Medium to strong current also helps keep organic debris from collecting, sweeping it towards the intake to be broken down within the FX6. A spray bar would be the perfect companion for this model. Spray bars let you create surface agitation for better gas exchange and disperses the outflow if you don’t want or need strong current.

Spacious Internal Volume

Aquarists generally buy canister filters because they allow for greater customization of the internal media. Instead of being stuck with a plastic frame for cotton and activated carbon (most power filters) you can choose lava rock, specialty resins, ceramic bio-rings, and much more.

The mechanical filtration area alone is a spacious 325.5 in2, plenty of room for foam media that will screen out large particles and house bacteria. But the real benefit is having a roomy compartment to house your nitrifying and denitrifying bacteria colonies.

While the process of reducing ammonia to nitrate (NO3-) is pretty well understood, not many aquarists realize that denitrifying bacteria are also part of the aquarium ecosystem.

Unfortunately, these bacteria are anaerobic, meaning they can live only in the lack of oxygen. The pore sizes of gravel, foam, and most ceramic media are too large to slow down the flow of water enough to prevent oxygen from entering. As a result, nitrate accumulates until it gets removed by water changes or plants.

However, by using media like Fluval’s Biomax in the FX6 we can complete the cycle. Our denitrifying bacteria finally have pores tiny enough to prevent much oxygen from entering. They then break down nitrate into nitrogen gas (N2) which then outgasses from the aquarium!

Spacious canister filters are the models of choice for reef aquarists, saltwater fish breeders, and other aquarists who keep nitrate-sensitive organisms.

Designed for Fast, Efficient Maintenance

While filtration is what it excels at the Fluval FX6 is designed for efficient long-term maintenance as well. For example, the filter includes a Purge Valve on the base so you can drain the filter without removing the lid.

The valve lets you also perform quick water changes and even add water back into your aquarium system without using buckets or siphon hoses!

Another feature is the Aquastop Valves on the top of the unit which allow for fast calibration of the output from maximum flow down to 0GPH. Usually, you’ll be making these adjustments when performing tank maintenance or if you need to reduce the flow or current in specific situations.

Being manufactured by the Fluval brand itself is also a bonus! Fluval Aquatics is world-renowned for quality products and parts can be sourced nearly anywhere in the world. Most aquarium and pet stores sell Fluval equipment and can order parts in the unlikely event of something breaking down.

However, if you need something down the road or your local store can’t assist, both Fluval’s own website and Amazon have parts for the FX6, including replacement impellers, motors, and other parts that tend to wear with time.

Starting the FX6 is also a breeze. Simply fill the canister unit, connect the hoses, and turn it on. The smart monitoring system will detect the air in the system and spend around 2 minutes purging water from within.

Maintaining the Fluval FX6

When you need to get inside the unit for maintenance, you’ll start by sealing the Aquastop Valves and releasing the lid clamps. Inside, there are several media baskets that you can lift out of the unit via a T-handle release. Simply lift, scrub, add, or remove media as needed for each of the three sections within.

While there is space for mechanical filtration in order to keep that from clogging too quickly the Fluval FX6 also has an anti-clog telescopic strainer. Especially large pieces of material, such as dead fish or leaves, are caught before even entering the mechanical filtration zone. Each time you do filter maintenance, you can easily pick out this debris.

And don’t forget the Purge Valve at the bottom of the unit. This feature speeds up simple water changes and emptying the FX6 when needed into a splash-free procedure.

Lastly, since we all forget to keep up with our monthly filter maintenance, the unit includes an indicator that lets you know at a glance the last time the unit was serviced!


The Fluval FX6 is by far the best canister filter on the market for aquarists with tanks 55 gallons or larger. While it works best for the 125-400 gallon community, the FX6 is also good for smaller setups that have advanced filtration needs, such as predatory fish or turtle setups.

The combination of powerful turnover, a spacious interior for customizable media, and easy maintenance are attractive and hard to find in competing brands and models. And best of all, using the Fluval brand means access to highly rated customer service and worldwide access to replacement components and media that’s tailored to the FX6.

Jason Roberts
About Jason Roberts
Jason is an aquarium fanatic that has been a fish hobbyist for almost three decades.

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