A seaweed aquarium feeder allows fish to feed on seaweed aquarium food while preventing escape of the food into the aquarium water. The feeder includes a base and hinged lid which closes against the base. The lid includes a recessed seaweed holding windowed area which fits over a protruding area of the base. The food is captured between the recessed seaweed holding windowed area of the lid and the protruding area of the base. Windows in the recessed seaweed holding windowed area allow the fish access to the food. A magnet pocket in the base holds a first magnet the feeder is held against an aquarium wall by cooperation of the first magnet with a second magnet outside the aquarium.