Various illustrative embodiments of an apparatus and method for reducing the dissolved hydrogen content of a molten metal alloy are provided. The disclosed embodiments can be utilized for the processing of molten metal alloys such as aluminum, and more particularly, for the removal of dissolved hydrogen from molten metal alloys such as aluminum. Gas permeable diffusers can be employed that are wettable by molten metal. When used as gas injectors, either in combination with ultrasonic oscillation or without, the gas permeable wettable diffusers can provide a high density of ultrafine inert gas bubbles that can be used to rapidly and efficiently reduce the level of dissolved hydrogen within the molten metal.