This FX4 guide from our reviewal team shall help you gain insight into the necessary features of the Fluval FX4 canister filter before you buy it.

Fluval is undoubtedly one of the best brands out there that deliver products of the utmost quality for fishkeeping. The Fluval filters FX series has been impressing people for several years now. The prime expectation of any customer before investing their money into buying a product is longevity. Of course, everyone wants the product to last for numerous years before being worn out and the Fluval FX4 canister filter fully justifies that. It’s plain black body with red and white strokes lining the different parts, provide it a unique and attractive look.

All points mentioned in this FX4 review will determine your choice and help you pick the best canister filter for your keeping fish situation.


fluval FX4 canister filter box components

Fluval FX4 Overall Rating: 9.1/10

⚠️Warning: In this category Fluval 407 scored lower (8.8/10) and SunSun HW-3000 scored lower (8.6/10). Make sure to check them out, to see the differences!


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Specifications of Fluval FX4

  • Dimensions (L x W x H): 15.75 x 15.75 x 16.5 inches / 40 x 40 x 42 cm
  • Biological Volume: 1.03 US liquid gallon
  • Filter Circulation: 450 Gallons Per Hour (GPH) / 1700 Liters Per Hour (LPH)
  • Filtration Volume: 3.69 US liquid gallon
  • Head Height: 2.1 meters
  • Mechanical Area: 1400 cubic centimeters
  • Motor Power: 30 watts
  • Pump Output: 700 Gallons Per Hour (GPH) / 2650 Liters Per Hour (LPH)
  • Aquarium Capacity: 250 US Gallons / 1000 Liters
  • Item Weight: 6.43 kilograms / 14.17 lbs

fluval FX4 external cascade canister filter

Box Contents Fluval FX4

So, to begin with, let us first introduce you to the FX4 box contents of the package our review team received.

  • Smart Pump
  • 2 baskets that can be stacked over one another
  • 3 types of multi stage filtration media- biological, chemical, and mechanical
  • Leak-proof valves
  • The 45° angled valves facilitate easy rotation and installation
  • Lid fasteners
  • Filter lid along with attachments
  • Telescopic strainer with anti-clog properties
  • Multi-directional output nozzles – these nozzles are extremely beneficial in controlling the flow rate of the pump.
  • Utility Valve with drain hose for quick maintenance and flushing of unit
  • Rim connectors, 3 clips, 2 O-rings and suction cup
  • Rubberized Feet
  • A connection port that allows you to easily attach the Fluval FX Gravel Vac (sold separately).

Fluval FX4 Features

FX4 components are easy to install and offer no such difficulty.

Now, coming ahead, let’s discuss its features one by one and see how they play a role in the efficient working of this FX4 canister filter.

The Fluval FX4 canister filter is full of amazing features that make it a first choice for the customers, but to keep the article precise yet relevant, we have tried to mention some of its exclusive features below that surely deserve your attention.

fluval FX4 multi stage filtration canister filter

Smart Operation Pump 

Lower FX series unit has an auto-start motor smart pump and after the addition of water, it starts by itself and pumps out 700 gallons of water every hour. The advanced microchip technology ensures the smooth working of the pump and effectively expels out the air. The speed and force of the rotor assembly are continually monitored to ensure maximum output and energy efficiency, optimizing the pump performance.

The pump draws up the water and passes it through various stages of filtration. The filtered water is then expelled by the pump into the aquarium in 4 major directions: inside-out, forwards-backward, top to bottom, and center-out.

Easy Maintenance 

No matter how good your product is, it will not last long if its cleaning and maintenance are not taken care of and undoubtedly, this process is a burden for the customers. But the delight while purchasing Fluval Aquatics FX series lower entry is that it is extremely easy to maintain.

To remove the lid, you just have to unscrew 8 screw clamps. After removing the lid, you have to lift the two red levers on either side of the filter baskets and then you can take out all the filter media inside and change or clean them as required.

To have access to the actual pump inside the filter, you will need a crosshead screwdriver to unscrew 3 screws, remove them and then get to the pump. Before removing the pump, just be sure that the canister is empty, or else the water will just destroy your pump. Also, do not misplace your sealing ring in the process as you will need it to assemble the stuff again.

This little process of maintenance and cleaning is not a grind and is least effortful as compared to the maintenance of several other filters. It only requires minimal time and minimal effort. The dial on the canister reminds you whenever it’s time to clean the filter.

High Performance 

The aspect where FX4 deserves a 10/10 is performance. The high performance of the filter is its’ hallmark. The process of filtration performed by the pump is excellent and the quality can be easily determined by the color of filtered water. The pump prevents contamination and keeps the water clean. The credit of the filtration can be attributed to the filter media incorporated inside it. The more is the filter media, the cleaner is the water. The multistage 5 layers filtration process provides a healthy environment for the aquatic animals and is evidence of its high performance. The good flow rate of the pump makes it a good choice both for large and small marine exhibits.

How To Set Up

Just like the other aspects of the Fluval FX4, setting it up is also not challenging at all. You don’t have to scratch your head to understand the technicalities as they provide you with a detailed user manual that can guide you step-by-step. Also, the instructions are explained in such a way that even an inexperienced person can complete the task like an expert.

The only section where you will encounter slight difficulty is setting the inlet and outlet tubes. In case they are too long, you can cut them at the desired length but just be double sure before you do that because you cannot undo it later.

Here are a few tips on how to put together a Fluval FX4:

  1. Take out all the filter media and clean them properly under conditioned water.
  2. Keep the bottom filter basket into the canister and affix the media, then again keep the top one inside and plug in the filter media. After adding the filter media, fix them into their place with the help of red handles.
  3. Pour in the water and close the lid. While closing the lid, diagonally tighten the screws (at opposite ends) and not circumferentially as it can prevent the lid from bending or lifting.
  4. Affix the inlet and outlet tubes and position them into the tank. The spray bar can be added at the end of the outlet tube if desired.


Yes, these few simple steps and you are all done with the Fluval FX4 setup! For a detailed guide about how to install Fluval FX4, you can go through the user manual provided along with the filter or browse the online instructions FX4 manual (item model number A214).

Tip: You would want to have your filter media go from coarse to fine and then setup your Seachem Purigen.

Fluval FX4 Operation Noise: Loud Or Quiet

Don’t judge by the size, as this external filter is comparatively very quiet and does not make a highly loud striking sound in the surroundings. Though the filter does create a minor alarming sound which will be majorly heard from the tank and not the filter, while it is evacuating the air inside diminishing accumulated air bubbles, happening every 12 hours, yet quiet noise operation is best most of the other competitors.

Filter Media 

The water flowing in the external filter passes through 5 different stages of filtration. To begin with, the water first undergoes mechanical filtration, wherein most of the debris is sedimented. The filtered water then passes through a biological foam pad (you can add 2 bio foams) and lastly passes through a chemical filter which is usually added at the bottom. It is practically always best to use chemical filtration as the last stage of filtration because it needs to be changed periodically and the cleaner it remains, the better it is. When chemical filters are placed at the last stage, most of the impurities in the water are filtered at the earlier stages and the water passing through the chemical filter is usually cleaner, and hence the longevity of the filter increases.

If you open the filter, you might notice some extra space left where you can incorporate additional filter media. People usually prefer to add Biomax media, water polisher, or an ammonia remover.

Coming to impediments, there is a little shortage of space in the filter baskets of the Fluval canister filter FX4 . Even if one forcibly jam compresses the baskets with the biological media, it would still not be enough for a 220-gallon tank. Hence it should specifically be used for smaller aquariums.

Self Primer 

Self primer is another feature that differentiates the Fluval FX4 external cascade filter from the rest of the filters. It does not ask you to take care of its priming, instead, it lessens your workload and does it all on its own. Isn’t that great? That’s exactly what this busy generation is looking for. And of course, you would know how important priming is for a filter, and how missing it could drastically affect the working of your motor.

Herein the smart Fluval FX4 canister filter, all you need to do is, add a little water before switching it on and then forget about it because it takes care of the rest thing itself.

The pump is functioned to readjust itself every 12 hours, but you do need to keep a count of this readjusting time as the alarm can be annoying and can even wake you up from a deep sleep. So, it’s better to keep a track of this evacuating time of the pump. And if it’s your first experience with a self-priming filter, then you should surely keep a note of this time as it can scare you in the earlier days.

Rest, there is nothing to be worried about as the alarm only honks for a few minutes, usually just one or two. As the alarm honks, the filter stops for a while, empties the excess air, and then restarts. This removal of air is very important for the proper functioning of the filter.

Purge Valve 

This is yet another magical feature of this external filter. The valve allows the attachment of Fluval FX Gravel Vac and additionally allows you to water change in the tank.

Isn’t emptying a tank a tedious job, where you have to move buckets of water forwards and backward? The utility valve of the Fluval FX4 canister filter works like a genie and saves you from the mess of buckets. It allows you to attach a hose to the utility valve and empties the tank in no time. You can keep the other end of the hose at a nearby window or in the sink.

Just remember to switch off the filter before emptying it, and rest the gravity takes care of the whole thing.

Now the drawback of the valve is that it can not help you in filling the tank. You will still have to use buckets for that purpose.

Ergonomic Design

The model is designed beautifully and is compact to perfectly find a place in small spaces. The exact measurements of the canister filter are as follows: 15.6 x 15.6 x 17.7.  It’s always good to cross-check the dimensions of the filters with the available space before purchasing it or else it’s only going to invite unwanted expenses later on.

Though nobody cares about the beauty of the filter as it is not a prime concern for anyone, yet with the purchase of Fluval FX4, you can be relieved about its appearance as it looks really good and has a very subtle and professional look.


  • It works well for both larger and smaller aquariums
  • The Self-priming feature is a blessing for the buyers
  • The utility valve makes it very easy to drain water from the tank
  • The installation process is a cakewalk
  • The maintenance process does not require much the effort


  • Limited space for filter media
  • The process of reassembling the lid can be a little arduous
  • Little expensive

Fluval FX4 Frequently Asked Questions (FAQ)

Below is a compiled list of answered frequently asked questions for Fluval FX4 cascade filtration system.

What’s The Flow Rate Of The Fluval FX4? 

In the case of larger aquariums, one wishes to find a filter pump that can diffuse approximately four times the total amount of water present in the tank. FX4 outside filter efficiently pumps around 700 gallons of water every hour, which is just great.

But this high efficiency of the Fluval FX4 cascade filter is not a constraint when it comes to smaller tanks because the larger water diffusion in the tank can help it stay clean. So, its high flow rate makes it a good choice both for aquariums and smaller tanks, even for huge fishbowls!

However, if you would still want to slow the flow rate of the Fluval Fx4 canister filter in cases of fish like bettas, here are some ways to do that.

How To Slow The Flow Rate Of The Fluval FX4?

1) Angle The Output Into The Sides

This one is truly the easiest and zero-cost method that can solve the issue of a high flow rate for you. You can angle the output nozzle into the sides, so it flows into the glass. This method drastically lowers the Fluval FX4 water pressure.

2) Attach Filter Sponge To The Output Nozzles

This DIY method requires a little effort but is quite simple to adapt. All you have to do is attach a filter sponge to the output nozzles and cut a hole in it. This effectively controls the flow rate as the sponge absorbs a little amount of water which indirectly slows the flow rate.

3) Add A Spray Bar

This is another DIY method in case you are good at innovations. Adding a spray bar is a cheap option that can diminish the water flow by altering a few strong currents into several weaker currents.

4) Close The Output Valve Slightly

This one is what people greatly follow to reduce the flow rate. However, closing it fiercely might damage the inside of the canister filter over some time but doing the same slightly can help you reduce the water flow inside the canister.

These wonderful methods can greatly slow down and control the flow rate of the water. Also, you can combine some of these methods to achieve the desired flow rate. Maje sure to also clean your FX4 impeller, otherwise you will need replacement of magnetic impeller assembly. Impellers assist control of water flow from your freshwater or saltwater tank to the canister filter, thus replacement is needed if it breaks.

What Size Tank for FX4? 

The Fluval FX4 canister filter can perfectly fit an aquarium as large as 200 gallons in size, but in case you are skeptical about its use in a smaller size tank, then here is the answer for you. The fact is that it can be perfectly used in smaller tanks if you inhabit the fish inside and you are creative enough. The FX4 concile the gap between the Fluval 406 and the Fluval FX6 external cascade filter, making it a great pick for tanks even for 150 gallon tank up to 250 gallon tank. So Fluval 406 vs FX4 and Fluval FX6 vs FX4 are the biggest rivalries for the FX4 depending on the volume of your reef tank or freshwater aquarium.

This Fluval FX4 canister filter would be best for any marine or freshwater tank from 55 gallons to 75 gallons to 90 gallons, actually this is the best canister filter for 75 gallon-tanks. If you have the right fish inside, then you can even use it in a aquarium as small as 50 gallons as long as the fish are comfortable with the flow rate of the water, for instance, a betta dislikes high and strong flow rates, so if you are thinking of utilizing this filter in a 50-gallon pump with betta inside, then it’s a complete no go. To still use this filter in such a case, you will have to consider the methods mentioned above to slow down the flow rate of the pump.

How to Prime Fluval FX4? 

You don’t need to worry about the priming of the filter as the Fluval FX4 has a self-priming feature, wherein you just have to add a little water before switching it on and then it takes care of everything itself.

How to Clean And How Often Fluval FX4? 

The first step towards cleaning the Fluval FX4 canister filter is unplugging it and then draining out all the water. Secondly, disassemble the lid and remove all the filter media, clean or replace them as required. And lastly, clean the empty external filter with water.

Coming to the question of how often it needs to be cleaned, the answer is a little unclear. Some prefer to clean the filter every 4-8 weeks, while some might skip the process for over 10-12 weeks. Since the aquarium also has some good bacteria that have several biological advantages, it’s not advisable to clean the filter or drain the water very often. To determine the right time to clean the filter, you can keep a count of the nitrate levels in the tank. Nitrate levels above 40 ppm can be toxic, so don’t let it shoot up and clean the filter on time.

How To Change Media For Fluval FX4? 

Changing the Fluval FX4 filter media is the most important step in cleaning the filter.  The first step is to drain the water, unfasten the lid, and take out all the filter media. The filter media can then be cleaned under conditioned water. You can even replace the media if required. And once you are done you can stack them back in the filter baskets.

What Size Tank For Fluval FX4?

Fluval FX4 is a universal filter, which can be used both in larger and smaller volume tanks. It’s suitable for tanks as large as 200 gallons and also for tanks as small as 50 gallons. Fluval FX4 cascade filter has a high flow rate and therefore, using it in a small fish tank might result in unbearable fishkeeping conditions but as long as you can slow down the flow rate, it will be all good. Also, FX4 for turtle tanks that usually get messy is a good candidate.

How To Clean Fluval FX4 Filter Hose? 

Apart from the cleaning of the Fluval FX4 high performance canister filter, one also needs to pay attention to cleaning the filter hose. The hose is a long pipe helpful in the drainage of the water, which is why a lot of dirt gets accumulated inside it over time. One should be careful enough while cleaning the pipe as a harsh hand might puncture it. The list of things required for the cleaning of the hose is a bucket of warm water, vinegar/H202, Teflon tape, and a hose brush. Moving the hose brush throughout the length of the hose can clean the debris amassed on the walls of the hose. You can also prefer to use a magnetic tube cleaner that reaches difficult areas of the tube and cleans the dirt mechanically. Or else, a sump pump could also be used for this purpose. If your hose is an extremely terrible condition you should consider getting a replacement hose part for your FX4.

Warranty Information

If your FX4 stopped working and troubleshooting hasn’t produced results, from the day you purchased Fluval FX4 external Filter, you will enjoy a 3 year limited guarantee. Only faults for which you are not accountable are legitimate. Please be aware that only then will non-replaceable items be replaced or fixed if the filter is returned along with all FX4 parts with a proper proof of purchase and paid bills. All the extra FX4 accessories and upgrades bought independently are bound to their own warranty. With the exception of the FX4 pump engine every part/addon/pad, and so on, produced for FX4/5/6 are interchangeable on all the FX series. So you can swap around parts through FX series except from the pump motor.

FX4 Review Recap 

So, after giving you a detailed insight into the Fluval FX4, here is a quick Fluval FX4 review recap to help you focus on the important features of this wonderful equipment. Don’t forget you can browse our best canister filter review to find all Fluval Aquatics competitors in the external cascade water filter category.

  • The flow rate is very high and in case you plan to use it in a small tank with bettas, you will have to slow down its flow rate with methods such as -angling it at the peripheries of the tank, incorporating a filter sponge into output nozzles, attaching a spray bar or else closing the output valve a little.
  • Filtration efficiency allows usage on tanks as large as 220 gallons or as small as 50 gallons in size.
  • The self-priming feature is magical and amazingly reduces your job.
  • The purge utility valve makes it very simple to change the water in the tank.
  • The maintenance of Fluval FX4 is quite manageable. Only Getting to the pump is laborious and requires the use of a screwdriver.
  • Setting up the Fluval FX4 is an uncomplicated process and the manual provided along makes it even simpler.
  • Cut short the input and output hoses carefully and precisely or else you might need new ones.
  • The Fluval FX4 is noisy only while evacuating the air from it’s inside and the noise only lasts for 2 minutes. This alarm honks every 12 hours so it might not be a good choice to keep it in your bedroom as it can scare you up.

The only minor issues associated with the Fluval FX4 are as follows:

  • Media baskets are slightly short for its’ design.
  • Reinstalling the lid is somewhat effortful.
  • Not all parts are compatible with acrylic tanks like the hose compartments.

Overall, our team did felt Fluval FX4 external cascade filter is a very good buy for up to 250 gallon fish tank, rating it at 9.1/10. Chick here to check the latest price FX4 for sale.


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