Plant, food residues and metabolic products deteriorate the quality of the aquarium water. Good water quality is necessary to promote the health of fish and plants in the aquarium. This can be achieved by aquarium filters. Filters draw in the aquarium water and pull out the pollutants and waste products from the water. Filters also provide an ideal habitat for bacteria that break down pollutants. The external filter is fully equipped and ready for connection. The built-in quick-start device and the filter start without priming offer easy installation. The filter media are also included in the scope of delivery. Due to the regular replacement of the easily accessible pre-filter, cleaning of the rest of the filter is rarely necessary. The large filter volume offers a high biological filter performance through various filter layers. The included biofilter balls have different diameters, which promotes the self-cleaning effect. Energy-efficient and safe with only 9 watts power consumption, the CristalProfi e702 offers high energy savings. With the same effective water circulation, the unit consumes less electricity than comparable predecessor models. The patented hose connection block with safety valve prevents water from escaping when the filter is disconnected.