Aqua-Tech Algae Magnet for Glass or Acrylic Aquariums Ideal for aquariums of fish or reptiles the Aqua-Tech Algae Magnet keeps your tank free from algae buildup with the use of two magnets. A felt-like surface covers one magnet on the inside and the magnet on the exterior can move it around. The algae comes off the fish tank magnet with thorough rinsing so you can use it again and again. Directions: Separate magnets and attach string to loop on each magnet. Before attachment make sure string length is slightly longer than the measured height of your aquarium. Position the yellow contact magnet on the inside of the aquarium and the green felt contact surface magnets on the outside. Magnets will bond through glass. Slide magnet over glass to remove algae spots. After use rinse yellow magnet thoroughly. Note if inside of the magnet detaches and falls to the bottom use the attached string to lift the magnet to the surface.