PROBLEM TO BE SOLVED: To provide a process suitable for high performance circulation cleanup for breeding water of a display aquarium.SOLUTION: In a process for circulation cleanup and clarification of breeding water through a filtration process, the filtration process has a biofouling carrier layer filled with a biofouling carrier other than sand with a filling thickness of more than 200 mm in the upper part, and a sand layer filled with sand with a filling thickness of more than 400 mm in the lower part. Breeding water passes through the bilayer filtration layer that the total of the filling thickness of the biofouling carrier layer and the sand layer is 600-1200 mm in a filtering rate of more than 20 m/h in descending current.
