Magnetic aquarium cleaners are a stroke of genius. You can wipe the inside of your aquarium glass clean without ever having to submerge your hand. The magnet adheres through the glass to the handle, which is used from the outside. It is important to remember not to get the magnet down into the gravel. If gravel gets trapped between the magnet and the glass, it will scratch the glass of your aquarium. Many aquarium owners leave the magnet attached to the tank when not in use.