Does anyone have any water filters that work very well in shallow water?

My current one (a ReptoFilter meant for turtle) works okay but I can see that it only filters out the debris in a 14inch radius. (From where it is in my aquarium it would need to cover a 17 inch radius to be effective)

Any ideas? (Preferably one with a link to something I can buy online but if not I can possibly find one this October when I leave my state.)

(Edit: I can always buy a second filter and place it in the opposite corner but.. that sounds like a waste.)