Flow Sensor - 1/4″ with push-fit connectors (FS-25) Usually used with aquarium accessories like RODI inputs, calcium reactor feed lines etc., this flow sensor can be placed in line with the flow on 1/4″ tubing, connected to the FMM, and communicate to your Apex the flow rate of water through that pipe. The flow sensor itself uses push-fit connectors to make connecting to your system as simple as possible. The FS-25 will work with flow rates from 3-12 gph. Return pump Measuring the flow of your aquarium's main return pump is an incredibly useful piece of information. The key benefit would be to have the Apex notify you the instant the flow stops for any reason - usually the result of a failed or faulty pump. Furthermore, an indication of a reduced flow rate could be used to determine that the pump or the lines are dirty or are becoming clogged with algae, debris, animals, or the growth of organisms inside your plumbing. Auxiliary pumps on reactors and the like This is a very handy application for the FMM. Place a flow sensor on a device like a carbon/gfo reactor and it serves many purposes. First off, you will know if your pump is not on or is faulty. Next, you can easily fine-tune the flow into the reactor by watching the dashboard tile on your Apex. Finally, you can know when the reactor is becoming clogged with detritus or possibly channeling has occurred by an alert on your Apex or by monitoring your dashboard. Put a flow sensor inline to your device, plug it in to the FMM, and see exactly the flow rate of the water (any aquarium fluid really) going through that sensor. The industrial-grade flow sensors work use either a turbine or paddle-wheel mechanism (depending on the model) to measure the flow.