A fluid mixing system and a method of using same for maintaining uniform concentrations of fluid chemical additives in a dilutant, in which the system includes a multi-port aspirator device including a venturi having a venturi inlet for receiving dilutant and a venturi outlet of reduced diameter for discharging said dilutant, a dilutant injector source fluidly coupled to said multi-port aspirator device for delivering a dilutant at a dilutant pressure thereto, and a plurality of injectate sources fluidly connected to the aspirator device at or immediately downstream said venturi outlet, wherein each said injectate source is capable of independently varying pressure at said a multi-port venturi injector with respect to said dilutant pressure. The use of the inventive fluid mixing system also provides a facile and accurate means of injecting required volumes of wet chemicals into a flowing stream of a carrier fluid.