hydro plants grow fast for more than one reason. Since the roots are immersed in water, the plant won't spend much energy looking for it like they will in a soil grow. The other thing is the oxygen level is raised, helping roots take up nutrients. Roots in soil get oxygen when the soil dries out. With DWC, the grower pumps air into the water which provides the necessary oxygen. Being always surrounded by oxygen and water in DWC, plants grow much more rapidly. The difficult part is the fertilizer, which is under the growers control, and many growers adopt the wondering about this or that, always second guessing if the fert is right. It's really not that hard, you just increased ppm levels to a max as the plant matures. The problem is knowing how much to use and when.