The invention relates to a method for stirring and/or aerating fluids, particularly sewage, having the following cyclically repeated steps: aerating the fluid by means of an immersed aerator for a predetermined first period of time (t1) using an aeration device (1) disposed on a carrier (3, 43) designed as a floodable hollow body (2, 42), the hollow body (2, 42) being flooded and air being brought into the fluid by the aeration device, whereby the potential for nitrification is created in the fluid; stirring the fluid by means of the immersed aerator for a predetermined second period of time (t2), the air infeed by the aeration device (1) being throttled or turned off, and the previously flooded hollow body being evacuated in order to fill the hollow body (2, 42) with gas or air, the immersed aerator assuming the function of a mixing device in which fluid rises upward, thus mixing the fluid, wherein the potential for denitrification is created in the fluid; and an immersed aerator.