A distributor plate for a fluid tank such as a water softener pressure vessel separates the resin bed from a lower end of the resin tank. The distributor plate includes a disk that is supported on an upwardly facing surface from below and that is restrained from upward motion by a weld bead located above an outer periphery of the disk. The disk may have an inner slotted plate portion and an outer portion, and wherein the outer portion of the disk has an upper surface having an annular protrusion extending above an upper surface of the slotted plate portion, with an upper surface of the protrusion forms an engagement surface for the weld bead. The disk may be formed from a thermoplastic material having a relatively high dimensional predictability such as high-density polyethylene (HDPE) and unfilled or 30% glass-filled Noryl®, respectively.