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TANK DECODED
Illustration of an internal aquarium filter fixed to the glass underwater in a planted tankIllustration
Filters · Internal filter

Fluval U2, taken apart

A quiet three-stage internal filter for small and medium tanks, if you can spare the space inside.

45–110L
Tank size
400L/h
Flow
5W
Power
View on Amazon UK What works and what doesn't

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Taken apart

Every part

Illustration of the filter taken apart: BioMax, foam pads, poly/carbon, flip-top cover, spray bar, magnetic impeller and motor
Illustration based on the official parts diagram, not a product photo.
The verdict

Works / doesn't

What works

  • Three filter stages in one body: foam pads, poly/carbon cartridges and BioMax.
  • Three flow options: top outlet, gentle spray bar or bottom outlet.
  • Two foam pads, so you never have to clean all the media at once.
  • Owners describe it as very quiet.

What doesn't

  • It sits inside the tank and takes swimming room, especially in small tanks.
  • Some UK buyers report receiving a 2-pin EU plug: check yours on arrival.

Care

  • Every week: rinse the foam, cartridges and BioMax in water taken from the tank, never tap water.
  • Never clean all the media at once: stagger it.
  • Every month: clean the impeller. Every 6 months: replace one foam pad and half the BioMax.
Specs

The numbers

Tank size45–110 litres
Flow400 litres an hour, adjustable
Power5 W
Media2 foam pads, 2 poly/carbon cartridges, BioMax
OutletsTop outlet, integrated spray bar, bottom outlet; venturi included
PlacementInside the tank, top outlet at least 1 cm below the surface
Warranty3 years
View on Amazon UK
Sources

Where this comes from

From our TikTok post “Inside the Fluval U2”. How we review.

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