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Neptune Systems PM2 Conductivity, Temp, I/O Expansion

Sku: NEP-PM2

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Neptune Systems PM2 Conductivity, Temp, I/O Expansion

Sku: NEP-PM2


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Real-time Monitoring of Salinity in Your Aquarium

Maintaining consistent salinity in your aquarium is key to the well being of every organism inside it. And, as busy as we sometimes are, we don’t even realize our parameters are out of whack until it’s too late. With this module, your Apex will be constantly monitoring the Salinity in your tank and will let you know the minute it is trending outside of the safety zone. 

And, there is an added bonus, you get an extra temperature port as well as six I/O switch inputs for use on ATO, feed buttons, leak alarms or whatever else you may come up with. Salinity varies with water temperature. This extra temperature port is extra important because, when used, it is coupled with the conductivity probe’s value to calculate the most accurate real-time salinity measurement possible.




  • Monitor/Control Conductivity/Salinity and temperature
  • 4 Measurement ranges (0-900 uS/cm, 0-9.0 mS/cm, 0-90.0 mS/cm, 0-50 ppt)
  • 6 digital inputs for dry contact switches- float switches, push buttons, pressure sensors, etc.
  • Full datalogging support in Apex Base module
  • Up to 240 AquaBus modules can be added to the Apex system
  • Plug and Play. Automatically recognized when installed into the system
  • Two AquaBus connectors for flexible expansion via AquaBus
  • Comes with 3′ AquaBus cable
  • Galvanic Isolation for accurate and reliable probe readings
  • Led Status Indicator
  • Upgradeable firmware
  • Compatible with all Apex systems


Purchase our optional I/O Breakout Box and you can monitor the off/on state of six I/O signals. This is useful if you want to set up an ATO (Auto Top Off), a feed button, or even a sump door alarm or light switch.


This is a topic other controller companies like to avoid. Why? Because not all monitoring ports are created equal. Galvanic Isolation is key to getting accurate readings on pH, Temp, ORP, and Conductivity. Some controllers either do not do it well (they are still figuring it out) or possibly not at all.

So what is Galvanic isolation? Well, the tech-answer is that it’s where two or more electric circuits must communicate, but their grounds may be at different potentials. It is an effective method of breaking ground loops by preventing unwanted current from flowing between two units sharing a ground conductor.

Now of course that is all geek-speak to most of us so let’s just put it this way: on a controller without galvanic isolation, your readings of pH, Temperature, ReDox (ORP), Conductivity/Salinity, etc. will be completely inaccurate.  Of course it costs us more to add this circuitry into the Apex, but what good is a controller if it doesn’t give you accurate readings?

Additional Information

Additional Information


PM2 Manual

Product Specs


Manufacturer Neptune Systems


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