Abstract: Apparatus (10) for attaching an object (O) to a sidewall (S) of an aquarium (A). A magnet (18) is attached to an object to be placed inside the aquarium. A niche or pocket (14) is formed in the side (16) of the object which will abut the inside wall of the aquarium. The niche or pocket is sufficiently large to accommodate the magnet which is affixed in place by any suitable means. A second magnet (24) is positioned on the outside of the wall adjacent the object. The magnetic attraction between the two magnets serves to hold the object in place, even if the object is positioned below the waterline (L) in the aquarium.