Magnetic floating cleaning devices are great tools for cleaning your glass or acrylic. These scrapers are sold in a variety of styles and are designed for several different glass and acrylic thicknesses. Going a little large on the magnet size can be good if you are an aggressive scraper, as it will keep the magnets attached to the aquarium better. But if the magnet is too large, the scraper will be hard to move and can even crack your tank if the two magnets come together too fast. On the other hand, if the magnet is too small or the aquarium is too thick, the magnet will have a hard time staying attached.