Fluval U3 Underwater Filter The Fluval U3 Underwater Filter is an internal aquarium filter for aquariums up to 40 US gallons / 150 L, offering 3-stage filtration, adjustable flow direction, and in-tank water movement for freshwater, saltwater, or compatible reptile setups. Internal Filtration for Medium Aquariums The U3 is designed for aquariums that need more internal filtration capacity than the U2 while still keeping setup simple and self-contained. It works well where external filtration cannot be installed, where supplemental circulation is needed, or where a fully submersible filter is preferred for a clean and compact installation. Fluval U3 Water Movement and Media Features 3-stage filtration supports mechanical debris capture, chemical filtration, and biological stability. Foam pads remove larger particles before water passes through the central media chamber. Poly/carbon pads help trap fine debris, reduce odours, and improve water clarity. BIOMAX media provides biological surface area for beneficial bacteria. Adjustable 3-way flow control allows top output, integrated spray bar output, or bottom output depending on aquarium needs. Flip-top lid gives quick access to media for cleaning and replacement without removing the full filter body. Vertical mounting creates current and circulation along the aquarium wall. Horizontal placement can be useful in shallow tanks, low-water setups, or decorative water movement applications. Fluval U3 Underwater Filter Specifications Item number: A475 UPC: 015561104753 Aquarium capacity: up to 40 US gal / 150 L Pump output: 155 US GPH / 600 LPH Wattage: 6W at 120 V / 60 Hz Dimensions: 10.5 in L x 3.25 in W x 4 in H / 27 x 8 x 10 cm Filter type: fully submersible internal aquarium filter Filtration stages: mechanical, chemical, and biological Mounting options: vertical or horizontal in compatible aquarium setups U3 Filter Application Notes The U3 is a practical primary filter for aquariums within its rated capacity or a supplemental filter for larger systems that need extra water movement. It is especially useful when the aquarium needs internal circulation, quick media access, and adjustable output without external tubing or cabinet-mounted equipment. Official Fluval U Series Video Setting Up the Fluval U3 Underwater Filter Rinse the supplied media, place it in the correct chambers, mount the filter securely inside the aquarium, and choose the outlet mode that best suits the tank. Keep the unit fully submerged during operation and rinse mechanical media regularly to maintain strong flow. What’s Included Fluval U3 Underwater Filter 2 foam filter pads 2 poly/carbon pads BIOMAX biological media
