a float actuated water level control valve has a sliding valve tube depending from a float to meter the amount of water flow through the valve proportionally in response to the position of the float . the valve is especially useful for controlling the water level in an aquarium overflow filter system . the valve inlet has an adjustable flow area which is defined as the area between a lower edge of the sliding valve tube and an upper edge of a drain . the configuration of the lower edge of the sliding valve tube and the upper edge of the drain are selected to provide increased flow area linear to the position of the float . the valve inlet is submerged , and drain gurgling sounds are thereby muffled . in addition , the valve maintains the water level within the reservoir at a height above the valve inlet , which is especially useful for reducing splashing sounds from water spilling over an overflow wall in an aquarium .