A dosage system for feeding a fluid (A) to a static mixer (1), said system comprising a tank (2) containing said fluid (A) at a predetermined pressure, a fluid passage (3) connecting said container (1) and tank (2), a control valve (4) provided within said fluid passage (3) to control the flow of said fluid (A) from said tank into said container; and a controller (6) for receiving a target flow rate (SP_Q) of said fluid (A), and an actual flow rate (PV_Q) of said fluid (A), and for outpurting a control signal (MV_L) to said control valve (4) indicating a valve position to adjust the flow rate. Further provided is a method for controlling said dosage system.