A water aerating device for an aquarium includes a housing having a chamber to receive a guide device which is arranged between an inlet and an outlet of the housing, a paddle wheel is rotatably attached onto the guide device, and a pumping device may be used to pump the water and to force the water to actuate the paddle wheel and to generate eddy current. Fresh air or carbon dioxide may be selectively pumped into the housing. A barrel may be used to adjustably attach the housing to the aquarium. A casing may be disposed on the barrel, to receive and collect dirt or protein carried by air bubbles that may be generated by the eddy current.