This is a Fluval U4 Underwater Filter Foam Pad (A488) for the Fluval U4 Underwater Aquarium Filter System (A480). This Fluval foam pad filter is used as the Stage 1 mechanical filter media in the Fluval U4 Aquarium Filter System.
The Fluval foam pad replacement for the Fluval U4 Underwater Aquarium Filter is made with porous foam to trap large particles, debris, and impurities such as dirt, sediment, dust, sand, rust, hair, limescale, and more. Fluval foam filters reduce the amount of particulate matter in your aquarium to help your aquatic pets thrive better and are especially suited for heavily populated aquariums.
The Fluval U4 foam filter replacement should be changed approximately every 2-3 months, though it can be rinsed clean between filter changes to extend filter life.
This Fluval U4 foam pad replacement filter is also known by Hagen part number A488.