A system and method for delivering silver ion biocide is described herein. The systems described relate to passing water from a water system through a silver ion release module and optional high-concentration silver ion release module. The system includes an analyzer, detector, and/or controller for monitoring the concentration of silver ion and adjusting the flow path, flow rate, temperature and/or pH of the water in order to obtain the desired concentration of silver ion. The system optionally includes other metal ions released into a water system, the concentration of which may be used to automatically calibrate the described system and/or cause the system to take actions based on the measured concentration of silver ion or of the second metal ion.