A cleaning device for aquariums comprises a water-tight enclosure configured to be submerged under water and a water pump comprising an inlet for receiving water and an outlet pipe for expelling water. The outlet pipe comprises a central axis. A power source is disposed within the water-tight enclosure for powering the water pump. An adjustable nozzle comprises a nozzle outlet in fluid communication with the outlet pipe, and the adjustable nozzle is configured to be rotated about the central axis of the outlet pipe to selectively adjust a position of the nozzle outlet. In one example, water volume flow or water velocity flow expelled from the nozzle outlet can be selectively adjusted via rotational adjustment of the adjustable nozzle relative to the outlet pipe.
