PROBLEM TO BE SOLVED: To provide a multipurpose water tank usable as a water tank in which eel fry or the like can swim freely through a treble layer, or usable as a water tank for water culture and having a water quality clarification function.SOLUTION: Water is supplied into a first-stage water tank A, a second-stage water tank B and a third-stage water tank C from a water supply/discharge port, and it is confirmed that water is supplied into the first-stage water tank A and the second-stage water tank B as much as 80% respectively, and each opening/closing valve of the first-stage water tank A and the second-stage water tank B is closed. Then, overflow from an opening/closing port of the third-stage water tank C is confirmed, and an opening/closing valve of the third-stage water tank C is closed, and thereafter each opening/closing valve of the first-stage water tank A and the second-stage water tank B is opened, so as to be opened as a gateway for fish in the water tank.SELECTED DRAWING: Figure 1【課題】三重層をうなぎの稚魚等が自由に行き来き出来る水槽として、また、水耕栽培用として、さらに水質浄化機能を持たせた多目的水槽を提供する。【解決手段】送排水口から一段水槽Ａ・二段水槽Ｂ・三段水槽Ｃへ送水し、それぞれ一段水槽Ａ・二段水槽Ｂの水槽に８分目入水したのを確認し、一段水槽Ａ・二段水槽Ｂの開閉バルブを閉め、その後、三段水槽Ｃの開閉口から溢れ出るのを確認し、この後、三段水槽Ｃの開閉バルブを閉め、その後、一段水槽Ａ・二段水槽Ｂそれぞれの開閉バルブを開き、水槽内の魚の出入口として開放する。【選択図】図１
