Filters · Internal
Fluval U3
Manufacturer-rated for aquariums up to 40 US gal; Fluval also suggests it as a second filter in larger tanks.
Internal filter that sits under water inside the tank, with foam, carbon and biological media and a three-way outlet.
Consider: It sits inside the tank, so measure the space it needs: 10.5 × 3.25 × 4 in, plus room to tilt it off its bracket. Fluval says it can lie on its side in a shallow tank.
US version, item A475. Check what’s in the box before you buy.
Tank size Fluval rates it for
Up to 40 US gal
Choose your tank to see where it falls.
Check it against your tank →Specifications that affect fit
- Manufacturer capacity
- Up to 40 US gal
- Power
- 6 W
- Supply voltage
- 120 V / 60 Hz
- Dimensions
- 10.5 × 3.25 × 4 in (L × W × H)
- Pump output
- 155 GPH
- Filter circulation
- Not published
- Maximum flow
- Not published
To see what it costs to run, enter the watts on its label and your daily hours in the electricity cost calculator.
Pump output, filter circulation and maximum flow are measured in different ways. Your filter will move less water than the box says once media and hoses are in. Measure it with the flow calculator.
Before choosing this model
- Check the water is deep enough to cover it, upright or on its side.
- Compare pump output only with other pump-output figures.
Our buying guides size it for these tanks:
A filter rated for your tank can still be too tall for your cabinet or too strong for small fish: see how to choose one.
Check it against your tank → Something not working? See the troubleshooting guide.
Choose and care for mechanical, biological and chemical media before buying replacement supplies.
Included items & upkeep
- foam pads (2)
- poly/carbon pads (2)
- BIOMAX (40 g)
Plan for the routine work
- Unplug before lifting it out of the water.
- Tilt it off its bracket and flip the top open to rinse or replace the media.
To budget for replacement media and supplies, use the first-year cost calculator. For how often and how to clean it, follow the maker’s manual.