a system for measuring and controlling the concentration of a chemical agent in a solution has a reaction cell for receiving a sample , a titrant dropper for releasing one or more drops of titrant into the sample , a first photosensor for sensing disruptions of light for every drop of titrant released , and a controller that communicates with the photosensor and computes the concentration of the chemical agent based on the number of disruptions of light at the photosensor . the present invention also includes a method for sensing and controlling the concentration of a chemical agent in a solution . the method includes having a sample containing the chemical agent , triggering the release of a number of drops of titrant into the sample , detecting the number of drops released into the sample , and computing the concentration of the chemical agent in the sample based on the number of drops of titrant released into the sample .