Present invention relates a suspendable magnetic brush for cleaning an aquarium with curved window surface, characterized in that an upper cover with an air chamber is attached tightly to a bottom cover with a cleaning material layer underneath, and an inner cover with a magnet located therein is provided inside the air chamber, said inner cover being attached to the bottom cover while isolated from the air chamber. Said upper cover having through holes connecting the air chamber to the exterior of the device. It is possible to adjust the air or liquid in the air chamber through the holes connecting the upper cover and the air chamber so that the weight of the interior magnetic brush can be adjusted so as to balance all the forces exerted upon the interior magnetic brush. As a result the interior elements of the brush can suspend in the water and move smoothly on the aquarium window upon the manipulation of the exterior brush. With the convex edge(s) of the bottom cover matching the curved window surface of the aquarium the magnetic brush can clean both curved window surface and the planar window surface as well.