Neptune Systems

FMM Fluid Monitoring Module

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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 into 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).


What's Included?

1x FMM Module

1x Aquabus Cable

More Information
UPC 019962171857
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Product Questions

How long is the aquabus cable that comes with this?
Question by: James Bulk on Apr 5, 2023, 2:30 PM
Hello, the aquabus cable with all the products are always 6 feet in length.
Happy Reefing,
BRS Customer service team
Answer by: Alexander Reinartz (BRS Staff) on Apr 7, 2023, 12:05 PM
Does the fmm module work over Wi-Fi or does it need to be plugged into apex pro unit or into an eb32 power supply?
Question by: mark Prieto on Feb 6, 2023, 11:05 AM
Thanks for reaching out! you can run it stand alone for an auto top off but anything else must be run through APEX
Answer by: James Johnson (BRS Staff) on Feb 20, 2023, 12:20 PM
Does this module still work with the A3?
Question by: Lisa Foster on Jan 29, 2023, 4:21 PM
Hey Lisa! It does however depending on the model A3 you get it is already built in!
Answer by: James Johnson (BRS Staff) on Feb 15, 2023, 3:18 PM
I just got a Neptune Apex and would like to add additional optical water sensors but am out of FMM ports in the Apex. Is this product the right way to add additional optical water sensor ports to my Apex?
Question by: Tom L on Jan 10, 2023, 4:56 PM
Hey there,
Thank you for reaching out to us. Yes, that is the correct module to add more optical sensors.

Please let me know if you need anything further and take care!
Answer by: Matt Lucero (BRS Staff) on Jan 12, 2023, 10:43 AM
Can the FMM be used with 2 leak sensors and a flow sensor as the same time or is it one or the other?
Question by: DanL on Dec 16, 2021, 5:10 AM
Thank you for your question. The FMM can accept 4 sensors. You can mix and match any of the sensors on the same FMM.
Answer by: William Glenn (BRS Staff) on Dec 16, 2021, 2:36 PM
What is the Difference between the ALD Module and the FMM Module that comes with the Leak Detection Kit
Question by: Jeff Willard on Nov 9, 2017, 6:39 PM
The ALD module is actually discontinued now, but it functions identically to the FMM module, but with a more limited functionality. The FMM module can have flow sensors, optical sensors, leak sensors, and even a pump attached to it, where the ALD was for leak sensing probes only.
Answer by: Charlie on Nov 25, 2017, 10:27 AM
Do you need a power supply if you have the Apex "Classic"?
Question by: Rory Bellina on May 8, 2017, 10:30 AM
Hey there,

You will not need a separate power supply from the Aquabus cable if you are just using this module for monitoring. However, if you plan to power accessories, you will need a power supply and plug this into the power port.

Happy reefing!
Answer by: Zack on May 12, 2017, 2:45 PM