A fluid treatment system .Iadd.and method .Iaddend.for changing the rates of growth of certain crystals and other solids formed within a fluid is disclosed herein. The apparatus includes a variable speed motor having a shaft, and a wheel assembly mounted on the shaft. The wheel assembly includes two circular ferro-magnetic disks separated from each other on the shaft a pre-determined distance to form a gap, and a ferro-magnetic spacer member concentrically arranged about the shaft and located in the gap between the disks. An array of magnets is concentrically arranged in a circular pattern about the shaft on the inner surface of each of the disks with the polarity of the inner pole faces of the magnets on one of the disks bang the same as each other and the polarity of the inner pole faces of the magnets on the other of the disks being the same as each other but opposite to the polarity of the inner pole faces of said magnets on the one disk. An elongated fluid conduit having a U-shaped non-magnetic portion is located in the gap formed by the disks between the inner pole faces of the magnets, the U-shaped non-magnetic portion of the conduit being hollow so as to have no obstruction for continuous fluid flow therethrough, wherein sufficient magnetic force is provided by the combination of the strength of the magnets, velocity of the fluid, and rotation of the magnets to accomplish beneficial effects on impurities in the fluid.