Plants, leftover food, and metabolic products deteriorate the quality of aquarium water. Good water quality is essential for promoting the health of fish and plants in the aquarium. This can be achieved through aquarium filters. The filters draw in the aquarium water and remove impurities and waste from it. Filters also provide an ideal habitat for pollutant-decomposing bacteria. The external filter comes fully equipped and ready for connection. The built-in quick start feature and filter start without priming allow for easy installation. The filter media are also included. Regularly replacing the easily accessible pre-filter means that cleaning the rest of the filter is rarely necessary. The large filter volume offers high biological filtration performance through various filter layers. The included biofilter balls have different diameters, which promotes the self-cleaning effect. Energy-efficient and safe with only 4 watts of power consumption, the CristalProfi e402 provides significant energy savings. With consistent effective water circulation, the device consumes 31% less power than comparable previous models. The patented hose connection block with safety valve prevents water from leaking when disconnecting the filter.