A sinker is provided to regulate the weight of a sinker body for buoyancy of a float by combining or separating first and second sinkers and to protect the quality of water and water plants by making a coating layer of thermosetting or thermoplastic resin. A sinker(10) is composed of a first sinker(11) equipped with a first ring(12) on the upper end and made of metal; a second sinker(13) equipped with a second ring(14) at the lower end and made of metal; and a connecting unit(20) for connecting or separating the first and second sinkers. The connecting unit comprises a male screw(21) protruded on one of the first and second sinkers and a female screw(22) recessed on one of the first and second sinkers.
