FIG. 1 is a top plan view of a nitrogen-removing aquarium filter showing my new design;

FIG. 2 is a side elevational view thereof, all sides being identical;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a cross-sectional view thereof, taken on line 4--4 of FIG. 2;

FIG. 5 is a top plan view of a second embodiment thereof;

FIG. 6 is a cross-sectional view thereof, taken on line 6--6 of FIG. 5;

FIG. 7 is a cross-sectional view thereof, taken on line 7--7 of FIG. 6;

FIG. 8 is a top plan view of a third embodiment thereof, the third embodiment is the same as the first except for a circular configuration;

FIG. 9 is a cross-sectional view thereof, taken on line 9--9 of FIG. 8;

FIG. 10 is a top perspective view of the original embodiment;

FIG. 11 is a side elevational view of the second embodiment thereof, all sides being identical; and,

FIG. 12 is a side elevational view of the third embodiment thereof, all sides, being identical.