A waterproof, non-toxic, and reusable filter media retaining cup having molded construction, a non-compartmentalized interior space, and a perimeter wall with a preferred slight top-to-bottom taper extending between a radial flange and an opposed bottom end having spaced-apart perforations and a non-perforated center area. The outwardly-extending radial flange depends from the top of the perimeter wall and spaced-apart slits through the perimeter wall's bottom portion extend to the bottom end and are preferably downwardly-widening. The bottom end perforations and wall slits in combination with the bottom end's non-perforated center area provide accelerated aquarium water turnover through contaminant-removing filter media retained in the non-compartmentalized interior space, while avoiding clogging and channeling that would otherwise slow the breakdown and removal of uneaten food particles and marine life bio-waste in the aquarium water, which in increasing concentrations becomes toxic to the marine life in an aquarium tank depending on it for survival.
