Method of purifying water in fish keeping water tank

Claim 1

A method of purifying water in a fish keeping water tank comprising: (A) circulating water at a rate such that at least half the volume of water in the tank is circulated per hour; (B) passing the water through a UV irradiation vessel providing UV radiation having a predominant wavelength of less than 280 nm, wherein the water is exposed to at least 170 μW·min/cm 2 of UV radiation at one pass through said vessel, or a given volume of water is exposed to a total of at least 1000 μW·min/cm 2 of UV radiation during a one-hour circulation of the water; (C) introducing the water into a first purifying tank having an inlet and an outlet and which includes a support cylinder wrapped with a first microorganism-growing bed of free-permeable nonwoven fabric made of synthetic resin and having a predetermined mesh size no smaller than 100μ, passing all of said water through said growing bed, to thereby bring the introduced water into contact with microorganisms and to separate some of said microorganisms from said growing bed, introducing said water into a space in said first purifying tank downstream from said first microorganism growing bed, where microorganisms separated from said first growing bed are suspended and grow, to thereby bring the water into contact with such microorganisms in said space; and introducing the water into at least one second purifying tank located downstream from said first purifying tank, each said second purifying tank having a free-permeable synthetic resin microorganism-growing bed.

Claim 2

A method of purifying water in a fish keeping water tank comprising: (A) circulating water at a rate such that at least half the volume of water in the tank is circulated per hour; (B) passing the water through a UV irradiation vessel providing UV radiation having a predominant wavelength of less than 280 nm, wherein the water is exposed to at least 170 μW·min/cm 2 of UV radiation at one pass through said vessel, or a given volume of water is exposed to a total of at least 1000 μW·min/cm 2 of UV radiation during a one-hour circulation of the water; (C) introducing the water into a first purifying tank having an inlet and an outlet and which includes a support cylinder wrapped with a first microorganism-growing bed of free-permeable nonwoven fabric made of synthetic resin and having a predetermined mesh size no smaller than 100μ, passing all of said water through said growing bed, to thereby bring the introduced water into contact with microorganisms and to separate some of said microorganisms from said growing bed, introducing said water into a space in said first purifying tank downstream from said first microorganism growing bed, where microorganisms separated from said first growing bed are suspended and grow, to thereby bring the water into contact with such microorganisms in said space; and introducing the water into at least one second purifying tank located downstream from said first purifying tank, each said second purifying tank having a free-permeable synthetic resin microorganism-growing bed.