Fluval FX6 vs FX4: Which Canister Filter?
Fluval FX6 vs FX4 compared on flow, media capacity, size and which tank size each suits, with a verdict on whether the FX6 is worth the extra.
The short version
Buy the Fluval FX4 for most tanks from about 75 to 150 gallons, and the FX6 for heavily stocked tanks of 125 gallons and up. Fluval lists the FX4 at 700 gallons per hour with 1 gallon of media and the FX6 at 925 gallons per hour with 1.5 gallons. The 400 and 250 gallon ratings are marketing ceilings, not filtration specs.
The FX4 and FX6 are Fluval's high-performance canisters, with Smart Pump technology that self-starts and clears trapped air. They share the same design, so the question is how much flow and media your tank needs. Use our filter turnover calculator to check.
Fluval FX6 High Performance Canister Filter
Under $500
Check price on AmazonAt a glance
| Fluval FX4 High Performance Canister Filter | Fluval FX6 High Performance Canister Filter | |
|---|---|---|
| Listed tank rating | Up to 250 gallons | Up to 400 gallons |
| Pump flow | 700 US gallons per hour | 925 US gallons per hour |
| Media volume | 1 US gallon | 1.5 US gallons |
| Height | 16.5 inches | About 21 inches (see our FX6 review) |
| Smart Pump | Yes, self-starting, auto air removal | Yes, self-starting, auto air removal |
| Budget tier | Under $500 | Under $500 |
Specs from each manufacturer's published listing. Confirm the current listing before you buy.
Choose the Fluval FX4 High Performance Canister Filter if…
Your tank is roughly 75 to 150 gallons and moderately stocked. It is shorter, so it fits under more cabinets, and it is the cheaper of the two.
Check Fluval FX4 High Performance Canister Filter on Amazon
Choose the Fluval FX6 High Performance Canister Filter if…
Your tank is over 125 gallons, very heavily stocked or full of messy fish such as cichlids or goldfish. The extra pump and half a gallon of extra media is the reason to pay more.
Check Fluval FX6 High Performance Canister Filter on Amazon
Who should skip both
If your tank is under about 60 gallons, both are too much; a Fluval 307 or a hang-on-back filter is a better fit. See Fluval 207 vs 307.
Related
Comparison based on published manufacturer specifications and the general consensus of owner reports. We have not tested these products side by side. Confirm current specifications and prices before buying. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you.
Frequently Asked Questions
Is the FX6 worth it over the FX4?
Only on larger or heavily stocked tanks. The FX6 pumps 925 gph and holds 1.5 gallons of media, against 700 gph and 1 gallon for the FX4. On a 75 to 100 gallon tank the FX4 is usually enough.
Can an FX4 run a 250 gallon tank?
Fluval rates it to 250 gallons, but 700 gph gives under three turnovers an hour on that volume before head height and media resistance. Treat the rating as a ceiling.
Do they fit under a cabinet?
The FX4 is 16.5 inches tall. The FX6 is taller, so measure your cabinet before you buy.
Are they self-priming?
Yes. Both use Smart Pump technology that starts on its own and clears trapped air every 12 hours.
How do I do a water change with them?
Both can drain through the output hose with the water change feature, which saves lugging buckets.
Planning or running a tank?
Use our free calculators and guides to get every number right.
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