A printhead assembly for an inkjet printer has a ink filter tower portion that contains filtered ink and includes multiple, substantially parallel extending elements. Settling of ink in an ink filter tower could clog the printhead nozzles and lessen the print quality. Therefore, in order to prevent the settling of the ink in the ink filter tower of the present design, a free-floating weighted slider is installed within the ink filter tower. The weighted slider has a top bridging member and downward-pointing shafts that are movable within trenches formed between the extending elements. During a reciprocating motion of the printhead assembly, the slider moves in a direction opposite to the direction of the printhead assembly and thereby agitates the ink within the tower. In addition to sliding from side to side of the printhead assembly, the slider may also be designed to pivot about an upper axis as it moves to further agitate the ink.