Abstract: An apparatus for mixing a solution includes first and second tanks, a sampling element, a flow control element and a mixing assembly is provided. The first tank has a first chamber and a first fluid inlet. The second tank has a second chamber. The sampling element is connected and communicated with the first chamber. The flow control element connects and communicates with the first chamber through the first fluid inlet. Two opposite ends of the mixing assembly connect and communicate with the first chamber and the second chamber, respectively.