Abstract: Diffusers on the bottom of a submerged header each include coarse bubble orifices which discharge a stream of air to form a bubble or film on the underside of a horizontal spreader at the edges of which the bubble is sheared by flowing water into multitudinous tiny bubblets rising in the surrounding liquid as a cloud. A second horizontal spreader, slightly above the first, has a similar action, shearing into fine bubblets any larger bubbles which escape from the first spreader to the second. Edges are staggered to supply air to different parts of the water flow. The rising bubblets set up a conventional rolling action in the body of liquid. It is this rolling action which produces the flow of water past the spreaders to shear the bubbles at their edges. A snap-in screw-tightened band secures each diffuser to the header.