Two Little Fishies' BettaMag Cleaning Magnet is an even smaller window-cleaning device than the NanoMag. It's designed for use on betta and goldfish bowls or pico aquariums. The BettaMag is sized just right for those small bowls and aquariums. It’s ideal for glass with a thickness of 1/8 to 1/4 inch. With glass aquariums you need to avoid trapping sand and gravel between the magnet and glass as it will scratch the aquarium. Do NOT use with acrylic aquariums.