The invention provides a dilution apparatus for a thickener of the type having a thickening tank and a feedwell disposed upstream of the tank to receive feed liquid, said dilution apparatus including: a receiving vessel adapted for at least partial submersion within the thickening tank to receive supernatant dilution liquid therefrom; and a submersible pump including an impeller adapted for at least partial submersion within the dilution liquid, the pump being adapted to transfer the dilution liquid from the thickening tank through the receiving vessel to the feed liquid for dilution thereof, before transfer of the feed liquid from the feedwell into the thickening tank. The pump is responsive to system parameters for adjusting the flow rate of the supernatant liquid.