Neptune Fluid Monitoring Module (FMM)The FMM (Fluid Monitoring Module) is a multi purpose module that, with the help of various accessories, enables your Apex to do: Flow Monitoring with the various flow monitoring sensors you can monitor the flow inside the pipes of your return pump, reactor, RODI feed, and much more Leak Detection plug in up to four leak detection probes and know you have a problem before it becomes a REAL problem Water Level Detection attach one to four optical water