DuoPad

The Seachem DuoPad is a non-scratch, dual surface algae pad for both glass & acrylic aquariums. The melamine foam side uses micro abrasive technology to easily remove algae from the sides of your aquarium, while the durable scrubbing side allows you to attack the rougher grooves of rocks and driftwood. It is particularly effective at removing algae from scratches. It is chemically inert and does not use soaps or detergents. It's white colour contrasts against dark algae making it easier to see when areas are fully clean.

More on Melamine:
Melamine foam is incredibly effective abrasive cleaner. It has a microstructure as hard as glass, but because of its open-cell structure it remains flexible. It performs on stains a lot like extremely fine sandpaper. In the aquarium, it easily removes algae by scraping with its extremely hard microscopic filaments.