Neptune Systems

FMK Flow Monitoring Kit

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$219.99 $219.99

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Know your Flow!

Do you ever wonder how much flow your pump is actually moving through your display, reactors, refugiums or anything else that is plumbed into your system.  The Flow Monitoring Kit (FMK) will unlock a world of control for any apex model!

Flow Monitoring Kit Includes:

  • FMM Module
  • 1" FS-100 Flow Sensor
  • 1/2" FS-50 Flow Sensor (Two Included)
  • Two 1" Unions
  • Four 1/2" Adapters


The FMM (Fluid Monitoring Module) is a multi-purpose module that, with the help of various accessories, enables your Apex to do:

  • Flow Monitoring
  • Leak Detection
  • Water Level Detection
  • Power 24VDC accessories
  • Future sensors


Return pumps

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

This is a very handy application for the FMM. Place a flow sensor on a device like a carbon/gfo/biopellet reactor and it serves many purposes. First off, you will know if your pump is not not flowing correctly or failed altogether. 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.

It is important to note that the flow rate that will be reported back to you from the flow sensors will likely be far lower than you expect or what is printed on the pump label or documentation. This is due to head pressure loss from physical height differences, long runs, restrictions such as ball valves, fittings like elbows, tees, and reducers, and then finally the loc-line many use as the entry point into their tanks. As an example, a pump rated at 3200gph will likely be showing less than half that amount in nearly all applications.

With the FMK – Fluid Monitoring Kit you get one 1″ Flow Sensor as well as two 1/2″ Flow Sensors. For North American customers, adapter fittings are also provided.
(The 1/2″ sensors are rated for flow rates from 30-250 gph. The 1″ flow sensors are rated for flow rates from 150-1500 gph.)



The FMK comes with three flow sensors but the FMM has a total of four ports. This means you have one port free to use for another purpose. Buy additional flow sensors (available also in 2″ and 1/4″ sizes) or choose from one of the options below and add even more functionality!



There are many useful purposes for water-level sensors on an aquarium. They can help you build an auto-top-off, monitor the levels in your supplement containers, even help automate saltwater mixing containers. Traditionally float switches have been the most commonly used types of these devices, however they are prone to all kinds of failure. On the other hand, the solid-state, optically-controlled sensors used with the FMM are much more reliable and dependable.

These optical sensors work by using an LED emitter and receptor in a clear enclosure such that when it becomes wet, the light bends and no longer completes the circuit.


Easy to use

Of course you could always add water-level sensors to your Apex – but it was more complicated than most users could handle. Now, with the FMM and these optical water-level sensors, you just plug them in! No wire-stripping, no breakout box necessary!



In addition to flow monitoring and level-detection, the FMM can be used for leak detection. Simply plug in up to four of our new, super-sensitive leak detection probes and place them where you want that oh-so-important protection for your floors, and your marriage! There is one sensor for solid surfaces and another slimline version for use under carpets.



The FMM has another trick up it’s sleeve. In addition to the four sensor ports, the FMM also has a DC24 accessory port and a power supply input. This adds another controllable outlet to your Apex set up. So, for instance, if you do want to make your own ATO and attach our available PMUP or Solenoid Valve, you can do so. Simply add our 36W 24V DC power supply (available separately).



More Information
UPC 019962170355
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Product Questions

How long are the sensors? I’m trying to figure out if I can fit one in my system. Also, if I add the ldk, does that use another module? I only have room for one more module on my apex jr system.
Question by: Gennifer Briggs on May 13, 2022, 6:17 AM
Hey there,
Thank you for reaching out to us. The sensor measures 4.5" and uses the FMM module.

Please let me know if you need anything further and take care!
Answer by: Matt Lucero (BRS Staff) on May 16, 2022, 12:32 PM
Is this compatible with apex classic or Jr?
Question by: Anthony Szurek on Jan 10, 2018, 12:32 PM
Thanks for contacting BRS!
The FMK is compatible with the apex classic and apex jr. Have a great day!
Answer by: Noah Winn on Jan 12, 2018, 10:32 AM
Is this compatible with apex classic
Question by: Anthony Szurek on Jan 6, 2018, 1:00 AM
Thanks for contacting BRS!
The FMK module is compatible with the Apex Classic controller. Have a great day!
Answer by: Josh Cuta on Jan 11, 2018, 1:05 PM
I didn't see anything in the literature about sensor orientation or the length of straight pipe before and after the sensor. I know some sensors are orientation-specific and the length of straigth pipe before/after the sensor greatly affects the accuracy. What's the requirements for the 1" sensor? Thanks.
Question by: Darrel B on Nov 3, 2017, 8:06 AM
Hey there,

Although Neptune doesn't specifically say, I wouldn't expect orientation to dramatically effect the reading on these sensors. Since water is being forced through the sensor at specific flow rates, it should read that same flow rate whether the sensor is oriented vertically or horizontally. :-)
Answer by: Randy on Nov 26, 2017, 9:47 AM
This kit comes with a 1" sensor for return line but mine is 1 1/2", should I still use the 1" or go up to the 2".
Question by: dave smith on Apr 18, 2017, 2:14 PM
Hey there,
It's always best to go up a size rather than restricting your return lines, so I would definitely go up to the 2" and then use reducers to convert to your 1.5" plumbing before and after the sensor.

Happy reefing!
Answer by: Zack on Apr 26, 2017, 4:53 PM