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ATKv2 - Automatic Top-Off Kit - Neptune Systems

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Product Description

ATKv2, ATK, or the Automatic Top Off Kit by Neptune Systems is now available and includes everything you need to maintain evaporation on your aquarium.  With three functions of redundancy it is the most precise and safe ATO system to use on your aquarium.  At Fragtastic Reef we always recommending using a top off system on your aquarium.  ATO systems like the ATK maintain not only a stable salinity but also all your other water parameters!

No Apex Controller is necessary when using the ATK! 

Look at all these features of the Neptune ATK:

  • Plug and play ready. No mounts to assemble. No bare wires to attach.

  • 3 Levels of Safety Protection!

  • Two optical water-level sensors (one for water level and one for emergency back up)

  • IQ-Fill water run-time intelligence – learns how much water you use at each top-off

  • Mechanical float valve prevents water overrun if electronics should ever fail

  • Does NOT rely on ANY fault-prone mechanical float switches, temperature sensors, or capacitive sensors!

  • Works Standalone (NO APEX NECESSARY!)

  • Advanced features are unlocked when connected to an Apex (i.e. remote failure notification via text, email, or iOS alert)

  • Includes PMUP, a powerful 24VDC pump that can push water vertically up to 14’

  • Audible failure alarm

  • Additional features with optional accessories


The ATK (Automatic Top-off Kit) is a simple, standalone, and complete solution for replacing water lost to evaporation.

The new aquarium hobbyist has many challenges, but none is more annoying than the chore of adding water, every day, to make up for that lost to evaporation (a.k.a. topping off/up).  This alone usually makes the automatic top-off (ATO) device the first piece of automation equipment purchased.

The ironic flip side of this decision is that a faulty ATO device is one of the leading reasons for catastrophic aquarium failure, or even worse, flooding of the house or business.

Not all ATO devices are created equal. Sadly, many ATO on the market are made with cheap components, have very little protection against these catastrophes, and are just a nightmare to assemble and install correctly.

An ATO does not have to be both a blessing and a curse!

We designed our ATK – Automatic Top-Off Kit to not only be super-simple to install and use, but it is unique in the market as an ATO device with three layers of redundant monitoring and water-level control. The ATK does the work for you, while at the same time protecting your tank and your home.

New Improvements for V2

  • New PMUP with improved longevity and reliability

  • Improved optical sensors

Here is the THREE Layers of protection on the Neptune Systems ATK:

1. Backup Optical Sensor

Should the main water level sensor fail, this second optical sensor is the backup. If water continues past the primary sensor, and then covers this one, the pump will be shut off and an alarm will sound.

2. IQ-Fill – Water run-time intelligence

If both the primary water sensor AND the backup optical sensor fail, the algorithm used in the ATK will not add more than double the learned water amount. It will shut itself off and sound an alarm.

3. Physical float valve – the final backstop

If for some reason all the electronic failsafes do not work, and water is continuing to be sent to the aquarium, the mechanical float valve is the safety device that will stop the water and prevent death to your aquarium and water on your floor.


  • FMM – Fluid Monitoring Module (runs standalone)
  • Pre-assembled water level mechanism with:
    • Magnetic acrylic mount (works up to 1/4″ glass/acrylic)
    • Two (2) optical water level sensors
    • Float valve
    • 90 degree tubing fitting
  • PMUP ATO Pump
  • 24V 36W power supply
  • 4m of orange RO tubing
  • 3/8″ -> 1/4″ push-fit adapter fitting
  • 1/4″ -> 1/4″ push-fit siphon break
  • Set-screw for non-float-valve applications



The FMM module included with the ATK has four ports for sensors and probes. The two installed optical sensors for the ATK only use port-1 and port-2. This means there are two free ports that can be used for these optional purposes:

Optical Sensors with Magnetic Mounts

Whether for your ATO reservoir, to use as a sump-high alert, or for your long term water storage such as a brute container, these optical sensors plugin into the FMM.  In standalone use when used in your ATO reservoir (plugged into port-4), the FMM will stop your PMUP and sound an alarm when the sensor is above the water level. If you plug it into port-3, and mount it high in your sump, if your water level ever goes that high, an alarm will sound and your PMUP will stop operating.


Leak detection with optional leak detection probes. 

Insert one of our leak detection probes into port-3 on the FMM and then place it near your sump. Now, if for some reason your sump should ever overflow, your ATK will stop operating and an alarm will sound.

Flow sensors in sizes from 1/4″ to 2″ (Apex-connected mode only)

Optional sensors are available that will monitor the flow through plumbing on your aquarium. This is perfect for monitoring the health of your return pump, keeping an eye on your emergency drain, setting the levels on your various reactors and filters, or watching the flow to your RODI.


Product Videos

ATK - Automatic Top-off Kit v2 Product Video 11:29

In this video, Terence introduces the latest version of the Neptune Systems Automatic Top-off Kit (ATK). Find out why the ATK v2 is the safest automatic top-off on the market. See what improvements have been made such as the new PMUP v2 as well as the improved optical sensors. ATK v2 Product Page:

  • ATK - Automati...
    In this video, Terence introduces the latest version of the Ne...

Product Reviews

Write Review

  1. very robust system, excellent product support from Fragtastic Reef

    Posted by Unknown on May 25th 2020

    My ATO broke 4 days before vacation. Panic
    Quick response and 2 day delivery Saved me. Was disappointed when the ATK didn’t work in standalone mode, but quick product support and hitting the reset button took care of the

  2. Monitoring my mixing station

    Posted by Jay on Aug 15th 2017

    I took the FMM from this ATK and decided to use it to monitor fluid levels in my mixing station with two optical sensors and a 1/4 inch flow sensor.. Now I know if something has failed and caused my RODI fresh water to be low and I also get alerted when my New Saltwater needs replenishing . I used the optical sensors that came with this unit with another ATK kit that I already had for my quarantine tank.

  3. I love this

    Posted by Jay on Aug 15th 2017

    This has simplified my ATO setup and integrated it with the Apex. Unlike my previous solution I now get notified if something is going wrong. Two optical sensors plus the manual float take redundancy to a whole new level.

    I have three of these. One for my main display and two quarantine tanks. I also use the extra port to monitor and tune flow to UV filters that I run on my quarantine tanks.


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Product Warranty

EVERY ITEM WE SELL IS BRAND NEW & COMES WITH A FULL MANUFACTURE WARRANTY! We do not sell used, defective, or returned product to our customers. Only exception to this is in our clearance and open box section of our website. Even those items still include a full warranty, and are usually an amazing deal if your looking to save money!

Most brands and products we sell have typically a 1 year warranty, with some products having up to 3 or more years. If you have any questions on warranties you can check the manufacture website or just contact us with any questions. At we sell only the best products, and only products we recommend and use ourselves, so you can buy with confidence.

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