referring now to the drawings , particularly fig1 showing the preferred embodiment of the invention , the present invention 10 will be understood to relate to a new device for maintaining stable water environment in a home aquarium 1 . the filtering and aeration device is contained within a cylindrical casing 11 that is made out of a water - impermeable and preferably transparent plastic . the unit 10 is vertically disposed in the aquarium 1 so that it is completely immersed in water and its top is approximately 0 . 5 inch below the water level 2 . an electrically driven impeller 12 powered by a battery or an external power source is secured at the bottom of the unit immediately under the perforated floor 13 of the lowest layer of the filtering cartridge 14 . the rotation of the vanes of the water - immersed impeller 12 develops suction by imparting centrifugal motion to the water . the delivery head 15 is maintained at a level that ensures a high turnover of water in the aquarium 1 . when water is sucked out of the lower section of the filtering cartridge 14 , it adiabatically forces an equal volume of water into the unit through its top cover 16 . this tightly fitting cover 16 has a plurality of fine apertures 17 through which the well - aerated water from the aquarium surface enters the unit . every aperture 17 becomes a site of a vortex 18 where water is accelerated and entrains additional air into the casing 11 . the apertured cover 16 breaks incoming water into droplets 19 . the droplets 19 fall freely through a section of the container 20 where the suction from below maintains a negative pressure . this section 20 serves as a degasification chamber . metabolic gases dissolved in water evolve therefrom and gradually leave the container 11 as they build up a sufficient pressure to break the water film at the vortices 18 . the large liquid - gas interface resulting from the formation of droplets 19 substantially increases the rate of the mass - transfer in the course of water degasification . degasified water droplets fall onto the top filtering layer 21 which is usually a ` pillow ` of fibrous floss material contained within a loosely woven sack 22 . similar sacks are used for all filtering media in the cartridge 14 because they are convenient for filter replacement . water droplets quickly trickle down to the lower filtering layers 23 - 26 . while the rate of flow coming into the unit 10 may be equal or even slightly higher than the outflow rate from the top filtering layer 21 , the surface of the latter is so highly porous that it is never completely covered with water . this creates an environment that is adverse to the growth of algae and therefore prevents biological clogging of the filter . the fibrous layer 21 is succeeded by layers of diatomaceous beads 23 and activated charcoal 24 , both with very large surface areas and high adsorption capacities . once most physical impurities have been retained by these filters , the water flows down to a layer of a nitrate anion - exchange resin 25 where chemical purification is accomplished . the bottom filter 26 is composed of calcite which is gradually leached by the water of various trace elements , the maintaining of a certain content of which in the aquarium water is important for sustaining aquatic life . well aerated , purified water replenished with trace elements is collected in the sump 27 and pumped out of the unit 10 near the bottom of the aquarium where it gradually replaces contaminated water . it is to be understood that the present invention is not limited to the sole embodiment described above , but encompasses any and all embodiments within the scope of the following claims .
a compact device for filtering and aerating aquarium water to sustain diverse aquatic species which comprises a suction pump and a non - submerged column of different filtering layers and in which water is initially dispersed into fine droplets that are given room to fall freely till water degasification is completed .