Devices and methods are provided for in-line water treatment using strong magnetic fields to influence corrosion, separate toxins, suppress bacteria and bio-fouling, as well as inhibit or greatly reduce mineral scaling due to fluid flow in or around equipment components. For example, a device is provided for applying a magnetic field to a portion of tubing through which a fluid flow, such as water, is conveyed. The device includes a number of links joined together via detachable pivoting connections, such that links may be removed and/or links may be added, thereby allowing a diameter of the device to be adjusted so as to accommodate larger or smaller piping, as necessary, for retrofitting applications. The use of magnetic treatment of fluids such as water may allow extended cycles of operation with higher concentration of mineral salts without the use of chemical scaling suppressants.