A support grid assembly for use in a vessel. The support grid assembly includes panels each including a first wall including a media-supporting screen and a second wall to be supported by the vessel wall inner surface. A manifold is coupled to the panels and is in hydraulic communication with vessel outlet. The manifold and the panels permit fluid to flow through the screen in each panel, through the panels, into the manifold, and through the manifold to the outlet of the vessel, as well as in the reverse direction. At least a portion of the first wall may slope downward toward the manifold, and at least a portion of the second wall may form a bottom surface that is curved to substantially conform to a curvature of the vessel wall inner surface. The panels may be arranged in a circular configuration extending radially from the manifold.