Fluval® U Series Underwater Filters provide complete and efficient 3-stage filtration, including BIOMAX biological filtering (U2, U3 and U4 models), to create superior aquarium water quality. 

The complete line, consisting of Fluval® U1, U2, U3 and U4 Underwater Filters, includes many practical and versatile features that make them ideal for application in fresh, marine and reptile environments.

Fluval U series filters provide the option of setting the flow output in 3 different positions, a key benchmark in underwater filtration. The Top Output setting provides maximum circulation and oxygenation, the Integrated Spray Bar setting provides a gentle, even flow for planted aquariums, and the Bottom Output setting is for Deepwater agitation. 

Fluval® U Filters also include a convenient flip-top lid that allows quick and easy access to the filter cartridge for maintenance or replacement.

In addition, Fluval® U Filters offer installation versatility: they can be installed vertically against the aquarium wall to create currents or customized flow patterns; or they can be placed horizontally in shallow water tanks or to create decorative features such as waterfalls.

The Fluval® U1 Underwater Filter is ideal for use in fresh, marine or reptile environments. Use the U1 as a primary filter in smaller aquariums or as a supplementary filter for larger aquariums. It is also ideal for tanks with low water levels. The U1 includes an adjustable flow control and comes complete with 1 foam pad.

Fluval® U1 is suitable for aquariums up to 55 L