With this Eheim battery-operated gravel cleaner (batteries ARE included), you can clean the base of your aquarium easily, even between water changes. The power of the device is so designed that dirt is taken up without disturbing the gravel and its purifying bacteria. A filter compartment in the device retains the dirt while letting the water immediately back into the aquarium. The filter element is simple to remove. Use only on gravel bigger than 2mm in diameter, The Gravel cleaner can be used in aquariums up to 60cm / 24 inches deep.