Water quality management device, water quality management method, and water quality management program

Provided are a water quality management device, a water quality management method, and a water quality management program with which it is possible to prevent the residual chlorine concentration in seawater from exceeding a reference value at a seawater discharge port. This water quality management device for use in a seawater utilization plant comprises: an attribute value acquisition unit that acquires an attribute value pertaining to seawater flowing through a condenser installed in the seawater utilization plant; a concentration prediction unit that, on the basis of the attribute value, predicts the residual chlorine concentration at a discharge port of a discharge path through which seawater is discharged from the condenser to the sea; a required amount calculation unit that, on the basis of the predicted residual chlorine concentration, calculates the required amount of a residual chlorine neutralizer to be injected into the discharge path; and a neutralizer injection unit that injects the neutralizer i