Fluval FX4
#3 in Over 150 galFull review
A powerful, efficient filter for big tanks, with a handy water-change valve. Treat the 250 gallon rating as generous and size by media need.
Amazon $337.99$337.99
The Fluval FX4 is the better aquarium canister filter overall, rated 3.4 to 3.3. The Fluval FX4 leads on turnover, efficiency and value. The OASE BioMaster 2 850 wins on media volume and features. The Fluval FX4 costs $42 less ($337.99 vs $379.99).
Prices were last checked November 9, 2026. Product prices and availability are accurate as of that date and are subject to change; the price and availability shown on Amazon or the retailer's site at the time of purchase apply. As an Amazon Associate we earn from qualifying purchases.
OASE BioMaster 2 850
#5 in Over 150 galFull review
The most media in one canister here. On tanks near 225 gallons, add a powerhead for flow.
Amazon $379.99$379.99
Which should you buy?
- Choose the Fluval FX4 for turnover (700 gal/h for up to 250 gal, 2.8x per hour vs 400 gal/h for up to 225 gal, 1.8x per hour), efficiency (23.3 gal/h per watt (30 W) vs 16 gal/h per watt (25 W)) and value ($1.35 per rated gallon ($337.99, up to 250 gal) vs $1.69 per rated gallon ($379.99, up to 225 gal)).
- Choose the OASE BioMaster 2 850 for media volume (8 L of media, 0.4 L per 10 rated gal vs 3.9 L of media, 0.2 L per 10 rated gal) and features (priming button or self-priming, shutoff valves, separate pre-filter, adjustable flow vs priming button or self-priming, shutoff valves, built-in UV, heater or water-change valve).
Scores side by side
Each factor is scored 0-100 against the same fixed reference points for every over 150 gal aquarium canister filter; a clear win is highlighted. How we rank explains each one.
| Factor weight | Fluval FX4 | OASE BioMaster 2 850 |
|---|---|---|
| Overall rating | 3.4/5 | 3.3/5 |
| Value 25% | 83 $1.35 per rated gallon ($337.99, up to 250 gal) | 71 $1.69 per rated gallon ($379.99, up to 225 gal) |
| Media volume 20% | 1 3.9 L of media, 0.2 L per 10 rated gal | 37 8 L of media, 0.4 L per 10 rated gal |
| Turnover 20% | 37 700 gal/h for up to 250 gal, 2.8x per hour | 8 400 gal/h for up to 225 gal, 1.8x per hour |
| Efficiency 10% | 100 23.3 gal/h per watt (30 W) | 62 16 gal/h per watt (25 W) |
| Features 15% | 70 priming button or self-priming, shutoff valves, built-in UV, heater or water-change valve | 85 priming button or self-priming, shutoff valves, separate pre-filter, adjustable flow |
| Warranty 10% | 50 3-year warranty | 50 3-year warranty |
Specifications
| Fluval FX4 | OASE BioMaster 2 850 | |
|---|---|---|
| Capacity | ||
| Rated aquarium | Up to 250 gal | Up to 225 gal |
| Pump output | 700 gal/h | 400 gal/h |
| Filter circulation | 450 gal/h | - |
| Turnover | 2.8x per hour | 1.8x per hour |
| Max head height | 6.9 ft | 7.4 ft |
| Media | ||
| Media volume | 3.9 L | 8 L |
| Pre-filter volume | - | 0.7 L |
| Canister volume | 14 L | - |
| Features | ||
| Primer | Yes | Yes |
| Shutoff valves | Yes | Yes |
| Separate pre-filter | - | Yes |
| Adjustable flow | - | Yes |
| Built-in UV | No | No |
| Built-in heater | No | No |
| Water-change valve | Yes | No |
| Power and build | ||
| Power draw | 30 W | 25 W |
| Warranty | 3 years | 3 years |