If you are looking for a canister filter for a big fish tank that can hold at least 250 gallons, then you most likely run into the FX series during your research. Fluval has released three models in the series so far with the FX4, FX5 and FX6. So which of these high performance canister filters are best suited for your fish tank? You can find out in our comparison guide below.
Since the FX5 is no longer available, you have to pick between the FX4 or FX6 if you want a high-performing filter for big fish tanks.
The FX4 is completely fine for aquariums that can hold between 100 to 250 gallons. With that said, the FX6 does provide more filtration as well as faster water flow. If you are planning to keep fish that prefers a lot of flow and/or planning to overstock your tank, then you might want to opt for the FX6 for aquariums between 100 to 250 gallons.
For aquariums that are more than 250 gallons and up to 400 gallons, then the obvious winner is the Fluval FX6.
You can also use both the FX4 and FX6 on fish tanks that can hold less than 100 gallons. With that said, you most likely have to reduce the water flow significantly if you are keeping fish that prefer a low flow rate.
You can purchase both products with the following links on Amazon:
- Fluval FX4 High Performance Aquarium Canister Filter
- Fluval FX6 High Performance Aquarium Canister Filter
We also recommend not using either filters for anything less than a 55 gallon long tank that is four feet in width. If you want a more advanced filtration system with more features such as the electrical conductivity monitoring, you may want to take a look at the Fluval G Series.
Fluval FX4 vs. FX5 vs. FX6 Comparison Chart
|Fluval FX4||Fluval FX5||Fluval FX6|
|Fish Tank Capacity||250 gallons (or 1,000 liters)||400 gallons (or 1,500 liters)||400 gallons (or 1,500 liters)|
|Pump Output||700 gallons (or 2,650 liters) per hour||925 gallons (or 3,500 liters) per hour||925 gallons (or 3,500 liters) per hour|
|Foam Surface Area||217 squared inches (or 1,400 squared centimeters)||325.5 squared inches (or 2,100 squared centimeters)||325.5 squared inches (or 2,100 squared centimeters)|
|Biological Volume||1 gallon (or 3.91 liters)||1.5 gallons (or 5.9 liters)||1.5 gallons (or 5.9 liters)|
|Filtration Volume||3.7 gallons (or 14 liters)||5.28 gallons (or 20 liters)||5.28 gallons (or 20 liters)|
|Filter Circulation||450 gallons (or 1,700 liters) per hour with filter media||563 gallons (or 2,130 liters) per hour without filter media||563 gallons (or 2,130 liters) per hour with filter media|
|Maximum Head Height||6.9 feet (or 2.1 meters)||10.8 meters (or 3.3 meters)||10.8 meters (or 3.3 meters)|
|Wattages||30 watts for 120V/60Hz |
30 watts for 230-240V/50Hz
|50 watts for 120V/60Hz |
48 watts for 230-240V/50Hz
|43 watts for 120V/60Hz
41 watts for 230-240V/50Hz
|Foam Filter Media||4x||6x||6x|
|Bio-Foam Filter Media||1x||None||2x|
|Biomax Filter Media||2x||None||2x|
|Carbon Foam Media||1x||None||1x|
|Auto Start and Self Priming?||Yes||Yes||Yes|
|Trapped Air Removal?||Every 12 hours||Every 24 hours||Every 12 hours|
|Twin Output Nozzles?||Yes||Yes||Yes|
|AquaStop Click-Fit Valves?||Yes||Yes||Yes|
|Lift-Out Media Baskets?||Yes||Yes||Yes|
|Pricing||Check price or buy on Amazon.||Discontinued||Check price or buy on Amazon.|
What happened to the Fluval FX5 High Performance Canister Filter?
Before we begin, let’s talk about the elephant in the room, which is the FX5 High Performance Aquarium Canister Filter. According to a user from Cichlid-Forum, a retailer explained that Fluval discontinued the FX5 and replaced it with the FX6.
Apparently, the FX5 has an issue where a buildup of wastes will slow down the pump. The FX6 also has other improvements that you will find out later on in this comparison guide:
Fish Tank Capacity
The FX4 has been rated for up to 250 gallons (or 1,000 liters). The FX5 and FX6 have both been rated for up to 400 gallons (or 1,500 liters).
The Fluval FX4 has a pump output of 700 gallons (or 2,650 liters) per hour. Both the FX5 and FX6 have a pump output of 925 gallons (or 3,500 liters).
Foam Surface Area
White foams are used inside all three canisters. The foams surround the media basket and act as mechanical filtration to trap incoming wastes from your fish tank. Beneficial bacteria will also grow on these surfaces, which will help remove ammonia and nitrites (both of which are toxic to your pet fish) from the water column.
The Fluval FX4 Canister has a total foam area of 217 squared inches (or 1,400 squared centimeters). Both the Fluval FX5 and FX6 Canister have the same total foam area at 325.5 squared inches (or 2,100 squared centimeters).
In terms of biological volume, the FX4 Canister Filter can hold 1 gallon (or 3.91 liters). The FX5 and FX6 can hold the same volume at 1.5 gallons (or 5.9 liters).
For filtration volume, the Fluval FX4 High Performance Aquarium Filter can hold 3.7 gallons (or 14 liters). Both the Fluval FX5 High Performance Aquarium Filter and Fluval FX5 High Performance Aquarium Filter can hold 5.28 gallons (or 20 liters).
When it comes to the circulation of water inside the canister, the FX4 is capable of moving 450 gallons (or 1,700 liters) per hour.
The filter circulation of the FX5 is 563 gallons (or 2,130 liters) per hour without any filter media aside from the aforementioned foam that surrounds the media baskets. If there are filter medias present, then the flow will most likely be reduced.
The circulation for the FX6 is also 563 gallons (or 2,130 liters) per hour although it has been rated with filter media. So the FX6 has the advantage over both the FX4 and FX6 when it comes to filter circulation.
Maximum Head Height
The FX4 Fish Tank Filter has a maximum head height at 6.9 feet (or 2.1 meters). The FX5 and 6 Fish Tank Filters have the same max head height at 10.8 meters (or 3.3 meters).
The FX4 uses the least electricity at 30 watts for both 120V/60Hz and 230-240V/50Hz frequencies.
The FX5 is more power hungry when compared to the FX6 as it uses 50 watts at 120V/60Hz as well as 48 watts at 230-240V/50Hz. In comparison, the FX6 uses 43 watts at 120V/60Hz in addition to 41 watts at 230-240V/50Hz.
Included Filter Medias
The included filter medias are different across the three models. You can check out the lists below:
- FX 4: 4x
- FX 5: 6x
- FX 6: 6x
- FX 4: 1x
- FX 5: None
- FX 6: 2x
- FX 4: 2x
- FX 5: None
- FX 6: 2x
- FX 4: 1x
- FX 5: None
- FX 6: 1x
- FX 4: 1x
- FX 5: None
- FX 6: 1x
As you can see above, the FX 6 comes with the most included filter medias while the FX4 has the second most. For the FX 5, you have to buy your own filter medias aside from the included foam. If you are looking for the best filtration types, you can take a look at our filter media guide for the FX Series.
All three FX High Performance Aquarium Canister Filters incorporate Fluval’s Smart Pump technology. Using an electronic circuit board, the canisters are able to monitor the speed and force of the water circulation to ensure maximum output and energy efficiency.
Auto Start and Self Priming
With the same Smart Pump tech, all three filters will be able to auto-start and self-prime without any need to manually pump water into the canisters. You simply only need to add water straight to the open top of the canister.
Trapped Air Removal
The FX filters also will also automatically stop momentarily to remove any trapped air from inside the canister. For the FX4 and FX6, this occurs every 12 hours. For the FX5, this occurs every 24 hours.
The FX4, FX5 and FX6 will then automatically restart again. This mechanism is used to ensure that the filtration remains most efficient.
All three canisters come attached with rubber feet at the bottom. These will reduce vibrations, making the filters quieter when running. They will also make the canisters more stable.
Twin Output Nozzles
The FX 4,5 and 6 also use the same twin output nozzles. This helpful tool will send water going out for the canister and into your aquarium in two different directions. As a result, you will have increased surface agitation and better water flow, both of which will keep your tank waters clean and healthy for your pet fish.
AquaStop Click-Fit Valves
All three also use AquaStop click-fit valves. Thus, assembling the tubing, as well as performing maintenance, to the canisters is relatively quick to setup as you only need to turn the valve lever. The click-fit connectors also simplifies taking apart and putting back the hosing as you only need to hear a “click” noise to know that the connection is secure.
All of the valves are designed to be water tight and shouldn’t leak any water. With the aforementioned valve lever, you can also adjust the flow in your fish tank.
Lift-Out Media Baskets
The Fluval FX4, FX5 and FX6 also use the same media basket type, which makes it easy to lift out of the canister, dissemble and re-assemble again.
All three models also use the same intake, which has been designed with anti-clog features to prevent any potential water flow issues that might arise from the accumulation of fish wastes. The intakes are also telescopic as you can adjust the length of the intake tubing.
The three also use a purge/utility valve that has been installed at the bottom of the canister. This valve will let you conveniently drain water from the canister.
FX4 and FX6: