In process control, precise level control of liquid in reaction vessels and storage tanks is essential. Tltis work attempts tlte designing, testing, developing and controlling of a coupled tank model using an online self-tuning model free fuzzy controller. This controller is able to intelligently learn, adapt and tune it-self such tltat it can track tlte desired set point with minimal error by adapting its rule consequents using plant's qualitative information only. Simulation results on some non-linear plants and experimental results on tlte real non-linear coupled tank system show that the error arising at tlte plant output can be greatly minimized if the correct value of monotonicity is identified. Real time controlling of tltis non-linear system by the adaptive fuzzy controller witltout any prior knowledge is evidence enough of tlte strength of this controller.