The seawater desalination process is emerging as a substantial source of fresh water by removing salt and minerals from an infinite supply of seawater effectively. The first stage in a desalination plant is the use of chlorine gas to sterilize the microorganisms in the water. During excess chlorine leakage, an alert is activated, employees are relocated away from the site for a specific period, and dampers will be manually opened. This will cause unsafe working conditions and a waste of time. To overcome this problem, this paper proposes a coefficient diagram method based proportional integral derivative (CDM-PID) control strategy for the tune the control parameter with the distributed control system (DCS) interfaced conical tank. During operation, a 10% NaOH solution is injected into the top of the scrubber column using an ethylene-ter-polymer (ETA) designed distributor to ensure that the solution is evenly distributed across the packing surface. The three control strategies are compared to tune the control parameter with the DCS interfaced conical tank. Instead of the sodium hydroxide tank in the chlorine scrubber system, this work presents the pilot plant of DCS interfaced with two conical tank interacting systems with different liquid level heights. Here, the proposed CDM-PID controller is compared with the standard Ziegler-Nichols (ZN)-ultimate cycling method, and the internal model control (IMC) method. The results demonstrated that the proposed CDM-PID approach is superior to existing approaches in terms of low oscillation, settling period, and high robustness.