<；P>；PROBLEM TO BE SOLVED: To provide a method for cleaning breeding water, which does not utilize a biodegradable plastic and safely, stably and continuously removes nitrate nitrogen by a simple operation. <；P>；SOLUTION: The method for cleaning breeding water includes a deoxygenation process for reducing the amount of oxygen dissolved in a certain amount of water contained in breeding water W<；SB>；2<；/SB>；collected from a breeding water tank T, a carbon dioxide dissolution process for dissolving carbon dioxide in breeding water W<；SB>；2<；/SB>；, a nitrogen fixation process for passing the breeding water W<；SB>；2<；/SB>；having passed through the deoxygenation process and the carbon dioxide dissolution process to a nitrogen fixation tank 3A composed of a filter medium assembly and packed with a microorganism carrier 32 and a breeding water supply process for supplying returning breeding water W<；SB>；3<；/SB>；having passed through the nitrogen fixation process to the breeding water tank T. <；P>；COPYRIGHT: (C)2010,JPO&INPIT
