Saim Aquarium Algae Cleaning Magnet Glass Aquarium Cleaner, Small This magnetic cleaner can be used on glass or acrylic tanks up to 0.12" - 0.39" (3 - 10mm) thickness Perfect design that flips from scrubber to scraper. Complete cleaning without using extra hand. Blades can be assembled easily. The plastic blade is suitable for acrylic tanks, and the stailess steel blade Use only on glass tanks Open Method: to rotate magnetic cleaner in the horizontal direction as the picture [because the Magnet is too strong, please do not pull up and down to open it ]