A device for infusion of gas into fluid, off gassing said fluid and returning said off gassed fluid to a body of fluid, comprising: an intake tube portion having an bottom opening submergable below a body of fluid so as to allow entry of fluid into said intake tube; gas diffusion means positioned within said intake tube below the top level of the body of fluid for infusing gas into fluid within said intake tube, to allow said gas to be infused into the liquid in said intake tube whereby the rising bubbles of infused gas are sufficient to drive the liquid in the intake tube upwardly to a top portion of the intake tube; a cross tube section in communication with said intake tube portion, said cross tube section extending to an off gassing section of or above said cross tube section; characterized in that the device is configured such that, when submerged to a predetermined depth in the body of fluid, the device fills with fluid to a top of the off gassing section which is located at a level above a surface of the body of fluid and above the cross tube section, thereby to generate a head differential; and further characterized by said off gassing section allowing said fluid to have surface exchange with the air and thus removal of gasses from the liquid; and a discharge tube portion communicating with the cross tube section, being positioned immediately below said off gas section and extending downwardly therefrom into the body of fluid, whereby the fluid entering the discharge tube has imparted a downward velocity due to the head differential between the liquid at the top of the off gassing section, pushing it down the discharge tube and back in the body of fluid. an intake tube portion having an bottom opening submergable below a body of fluid so as to allow entry of fluid into said intake tube; gas diffusion means positioned within said intake tube below the top level of the body of fluid for infusing gas into fluid within said intake tube, to allow said gas to be infused into the liquid in said intake tube whereby the rising bubbles of infused gas are sufficient to drive the liquid in the intake tube upwardly to a top portion of the intake tube; a cross tube section in communication with said intake tube portion, said cross tube section extending to an off gassing section of or above said cross tube section; characterized in that the device is configured such that, when submerged to a predetermined depth in the body of fluid, the device fills with fluid to a top of the off gassing section which is located at a level above a surface of the body of fluid and above the cross tube section, thereby to generate a head differential; and further characterized by said off gassing section allowing said fluid to have surface exchange with the air and thus removal of gasses from the liquid; and a discharge tube portion communicating with the cross tube section, being positioned immediately below said off gas section and extending downwardly therefrom into the body of fluid, whereby the fluid entering the discharge tube has imparted a downward velocity due to the head differential between the liquid at the top of the off gassing section, pushing it down the discharge tube and back in the body of fluid.