This glass pane cleaner avoids scratches on internal glass panes, and can therefor even be used on acrylic glass panes with the small plastic blade.
The inner magnet is more than 3 mm (.2 in.) away from the glass and thus prevents the jamming of the sand. The two plastic blades remove the algae considerably better from the glass panes than a flat cleaning surface - almost as good as a sharp metal blade. The life of a blade is from several months up to approx. one year. The low flow resistance during the cleaning with a simultaneous high magnetic coupling, makes a separation of the magnet nearly impossible. 
The large blade should only be modified with the included stainless steel blade for aquarium glass panes with particularly tough algae, e.g. older deposits on the side walls or thick calcareous algae.

For panes with a glass thickness from 6 mm (1/4") to max. 10 mm (3/8"). 
Width 45 mm (1.77 in.), length 78 mm (3 in.).
Including a replacement plastic blade.