The Complete Fluval FX6 Review

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For all their beauty, large fish and the large aquariums they need can be a hassle to maintain. With as much waste as these animals create it takes a powerful unit and carefully chosen media to keep things clean. 

Otherwise, ammonia and other metabolic byproducts build up to toxic levels, killing your sensitive and often expensive show specimens!

Once you start going beyond 125 gallons traditional hang on the back power filters simply aren’t up to the task. Instead, I recommend taking a look at high-capacity canister filters like the Fluval FX6 Canister Filter.

Things to Consider Before Buying a Canister Filter

Canister filters are some of the most capable filtration units on the market. Flexible in design, powerful in how much water they can filter, and often silent, they are well worth the cost over traditional power filters.

However, there are a few things to consider when searching for a new canister filter:

How Much Water Turnover Do I Need?

While very capable, most canister filters are overkill for aquariums smaller than 30 gallons. The small bioload of small aquariums makes them impractical in terms of cost versus power filters unless you simply want the very best filtration possible. 

Canister filters are significantly better for larger aquariums because not only do they turn over water faster but don’t expose water to the air, reducing evaporation potential.

How Much Space Do I Need for Filter Media?

The larger the compartments the more room you have for the infinite variety of media options available to canister filters. 

If you want to stack multiple types (i.e. pumice for biological filtration, resin for chemical filtration, etc), a large canister filter is needed to hold all of these materials.

How Easy is it to Find Media & Replacement Parts?

Canister filters are made by a number of brands. However, off-brand filters can be difficult or impossible to find parts for if something goes wrong. Parts and support for name-brand models like Fluval and Marineland are much easier to source.

Fluval FX6 Review

If you’re like me, you’re looking for a high capacity filter with plenty of storage space for customizable media. And by choosing a name brand filter you get the best customer support possible for possible issues. 

The Fluval FX6 is the second of the two filters in the FX line, alone with the smaller FX4. Both are the top of the line models Fluval makes for aquariums 125 gallons in size and larger.


  • 925 gallons per hour pump output = very high turnover rate
  • Rubberized footing for quiet operation
  • Smart Pump design that monitors flow and power usage for optimal performance
  • Holds approx. 1.5 gallons of filter media & includes media to start you off
  • Easy setup and operation


  • Large capacity makes the unit heavy
  •  Included media doesn’t have pores for anaerobic (oxygen-hating) bacteria
  • Air purging system sometimes unreliable

Features, Specs, and Benefits of the Fluval FX6

523 GPH Turnover Rate

While the pump outputs 925 gallons per hour (GPH) the filter turns over 523 gallons of aquarium water per hour. Therefore, the Fluval FX6 is rated for aquariums up to 400 gallons in size. 

Many hobbyists also use them for smaller amphibian and reptile setups, which need more powerful filtration thanks to the large amounts of waste these animals create.

Best of all, despite the extra power of the FX6 it actually uses 10% less power than older generation models. This comes thanks to advances in motor technology as well as a smart monitoring system that monitors water flow, power usage, and air contained in the system to efficiently regulate output.

The high turnover rate also allows you to create sections of the aquarium where strong currents hold sway, similar to a powerhead. Filter feeding organisms like bamboo shrimp or crinoids will typically place themselves near the outflow to pick up suspended particles. 

By positioning the outflow properly you can create surface agitation to facilitate additional oxygenation. The nozzles can also be directed in several places simultaneously to mix the water enough to help keep loose organic debris in suspension long enough to be taken up by the filter.

Unfortunately, Fluval doesn’t make a spray bar for their FX canister filters, which aid gas exchange and disperse the outflow if you don’t want a strong current. However, there are several DIY methods for creating one if you prefer that design! 

Large Internal Capacity

Another major benefit of the Fluval FX6 is the internal storage space: the unit provides enough room for 1.5 gallons (5.9 liters) of filtration media. Typically, canister filter owners will mix their favorite mechanical, chemical, and biological filtration products to polish aquarium water. 

The mechanical filtration picks out suspended particles, the chemical media removes inorganic toxins and heavy metals, and the biological media cultivates bacteria that nitrify and de-nitrify ammonia byproducts.

Denitrifying bacteria are especially important and something few aquarists consider. These bacteria are anaerobic, meaning they find oxygen poisonous. The larger pores most biological filtration media contain provide too much flow and don’t allow anaerobes to colonize. 

In a spacious canister filter, there is room enough to provide both regular and fine-pored media to achieve full denitrification of nitrate (NO3-) into nitrogen gas (N2). 

This is important because while nitrate is the least toxic byproduct of ammonia and is typically removed by water changes, many marine fish and invertebrates are very sensitive to even slight amounts.

Large canister filters also provide space for a variety of chemical filtration methods. Hang on the back power filters typically only have room for a single variety, like activated carbon. 

The Fluval FX6 has enough room for not just activated carbon but specialty media like their silicate, nitrate, or ammonia-absorbing resins that can target specific water quality issues.

Rubberized Footing & Quiet Motor

While subtle the rubber molding attached to the base is a key advantage of the Fluval FX6. This coating muffles vibrations coming from the pump that would otherwise cause the unit to be noisy. 

Sounds can still be amplified if placed on, say, a wooden stand with a raised floor. But this is still one of the quietest high-capacity canister filters on the market right now. 

The water pump’s motor is also optimized for silent running. Comparable in sound to a laptop fan, you really need to be listening carefully to pick it up. The water moving through the tubing can actually be louder than the pump itself! 

Some gurgling can occur if air needs to be flushed from the system, which is done automatically every 12 hours to maintain as perfect a vacuum as possible.

Valves and Seal Aid in Weekly Maintenance

The Fluval FX6 is designed to aid aquarists with more than just filtration. Several design features help expedite weekly and monthly maintenance, like the Purge Valve located at the base of the unit.

Not only can you drain the filter without removing the lid, but you can also use it to make simple water changes and add water back into the aquarium system without resorting to buckets. 

Aquastop Valves on the top of the unit adjust the output of the pump from the maximum setting down to 0GPH as needed. This is typically done for maintenance needs or simply to lower the amount of current and aquarium turnover.

Fluval Parts & Customer Support

As a major aquarium supply brand Fluval has supply chains worldwide. Parts are easy to source from both local aquarium stores and the manufacturer itself. Fluval’s customer support is also excellent and responsive in terms of giving advice on issues and honoring warranties when needed.

However, if you already know precisely what you need, even Amazon has you covered, carrying replacement motors, impeller assemblies, and other parts for the FX6 that can wear out over time. 

Setup, Cleaning & Maintenance of the Fluval FX6

Setting Up the Fluval FX6

Canister filters can be a hassle to set up. Often they don’t come fully assembled and require you to put together a variety of components. Once that’s finished, you’ll need to fill the unit with water and prime it by expelling air from within, which can take ages.

The Fluval FX6 is a self-priming unit. No more sucking on hoses or shaking the unit in an effort to remove all of the internal air bubbles! Simply fill the FX6 with water, plug the unit in, and additional water will get pulled in. 

The electronic circuitry will detect and eliminate internal air bubbles within a few minutes. It also stops running for 1 minute to release collected air on a 12-hour cycle, leaving you with a silent running, easy to install unit.

Cleaning & Maintaining the Fluval FX6

Once you seal the Aquastop Valves and release the locking clamps you have full access to the innards of the FX6. The media baskets are accessible directly, lifting out of the unity with a T-handle release. From there you can add, remove, and clean each of the three sections as needed.

To prevent the media from clogging too quickly the Fluval FX6 includes an anti-clog telescopic strainer to prevent the largest pieces of debris (dead leaves, etc) from entering the filtration unit itself. This strainer can simply be rinsed each time you do filter maintenance.

As mentioned before the Purge Valve at the base of the Fluval FX6 also aids maintenance by allowing you to empty the unit before opening it or even perform splash-free aquarium water changes.

And just in case you’re the kind of aquarist who misses monthly maintenance on occasion the FX6 has indicators on the lid that reminds you when it’s due for a cleaning!


If you’re an aquarist who needs the absolute best water quality for your corals, sensitive fish, or messy reptiles, high capacity canister filters like the Fluval FX6 are the obvious choice. 

By giving you so much room for customizable filtration media and a high water turnover rate, your animals will thrive, ensuring you’re spending less time on maintenance and more simply enjoying your pets!

Also, remember that the design of the FX6 unit also speeds up weekly and monthly water changes and other maintenance needs. While large the Fluval FX6 ensures as stress-free an aquarium experience as possible for aquarists with the biggest tanks! 

If you’re interested in picking up a Fluval FX6 for yourself, have a look here!