Pax Bellum LLC

Pax Bellum ARID N18 Macroalgae Reactor - For Tanks 40-120 Gallons


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What’s a Pax Bellum A.R.I.D. N18 Reactor and how does it help my reef? Find out here!

This ingenious device utilizes macroalgae (specifically Chaetomorpha) to function as a nutrient export mechanism. The unique design of the ARID incorporates a coaxial LED light array housed in a tube to maximize light penetration and efficiency. Vapor heat pipe technology keeps the LEDs running cool for maximum light emission and lifespan while keeping the heat out of your aquarium. The LEDs were selected to supply intense PAR (photosynthetic active radiation) for rapid macroalgae growth. Maximum nutrient uptake is ensured by pushing system water evenly through the macroalgae mass.

Eliminate the clutter around your aquarium the ARID can function as a stand-alone filtration system. Designed to replace GFO (granulated ferric oxide), nitrate reactors, bio-pellet reactors, carbon dosing and even protein "skimmers" (foam fractionators). The ARID can perform functions the previously mentioned equipment can`t. Functions such as, increasing and stabilizing Ph from day to night, lowering dissolved CO2 concentrations, keeping dissolved oxygen even from day to night, and increasing dissolved oxygen to levels higher than can be attained with skimmers alone, all standard benefits of running the ARID system.

Small but mighty… The N-series (aka Nano series), N18 and N24 with its acrylic construction, are marketed for the aquarist that collects and displays their kit just as passionately as they collect and display the organisms residing within the main display. The aquarist can easily remove the light cover to reveal the inner workings of the opaque acrylic chamber and inspect the growth of the macro-algae inside. Highly polished acrylic edges are found throughout the N-series. The N24 has additional chamfered edges on the lid, flange, and base. The profile of the N24 mirrors that of the C-series while the N18 striving for the smallest envelope forgoes the recognizable ARID gear shaped profile for a more simple and compact form.

For the aquarist with a system from 40-120 US gallons (150-450 liters) the N18 is the smallest practical use of the ARID reactor embodied in a H.O.T. version. This model stands 16- 3/8” tall, and has a footprint of 6- ½” in diameter; the chamber and lid are produced entirely out of cast acrylic. The H.O.T. bracket is integral to the chamber flange and is adjustable for tank rims with bracing. The central inlet port on the bottom is ½” barb, as is the outlet on the lid. LED power consumption is 12 watts. Optional in-line quick-disconnects are available for the N18 separately. The N18 ships with starter solutions, 125ml of a 5% w/v solution of Nitrate+Molybdenum and 30ml of Iron+Manganese. To contain the blinding light emanating from within the reactor included is a magnetically fastened removable light blocking chamber cover.

Have a calcium reactor? Both the N18 and N24 can accept the same optional calcium injection assembly. This plumbing kit threads directly into the water inlet on the base of the N24 and placed inline with the supply tubing on the N18. The assembly and can be installed or removed at any time by the aquarist. This add-on kit functions by creating a high pressure ¼” push-fitting port and low pressure ¼" push-fitting port by separating the two ports by a user preset valve. The valve is a union that accepts restriction discs with different port sizes to create the desired back pressure to send water to a calcium reactor. The effluent coming from the calcium reactor passes through the check valve and drip counter included in the kit, then enters the ¼" push fitting port on the low pressure side of the calcium injection assembly. This is the port below the union containing the restriction disc. There the calcium reactor effluent mixes with the bulk of the water entering the ARID, and makes contact with the macro-algae where it is stripped of excess CO2 and phosphate before entering the reef system.

Do not use in conjunction with; carbon dosing, nitrate reactors, bio-pellet reactors, GFO (granulated ferric oxide)

Pax Bellum solutions should be used to run the ARID system successfully.

Recommended Dosage

Nitrate & Molybdenum
1ml raises 100L 0.5ppm
Does as needed to maintain NO3:PO4 ratio of approx. 100:1

Iron & Manganese
1 drop per 25 gallons daily.


  • System Size: 40-120 gallons aquariums
  • Body Material: Cast Acrylic with Tyvek cover (to keep light inside)
  • Total Height: 16.5"
  • Recommended Flow Rate: 150-200 gallons per hour
  • Recommended Pump: MJ900 Pump or equivalent
  • Total Footprint: 6.5"
  • Hose Inlet/Outlet: ½" FNPT hose (hose and pump not included)
  • LED Power Consumption: Standard 110v / 14 Watts
    • The supplied power supply can handle 220v input power with the use of a simple adapter cord to connect to the wall socket—mainly for European use


Can be placed within the sump if the tyvek wrap is kept above water. It is highly water resistant but submerging it is not recommended) As with any electrical device use caution and always unplug it when working in the sump area.

Product Manuals & Documentation

Pax Bellum ARID N18 Macroalgae Reactor - For Tanks 40-120 Gallons

Owner's Manual available for download in Adobe PDF file format

Pax Bellum ARID N18 Macroalgae Reactor - For Tanks 40-120 Gallons

Additional Info 1 available for download in Adobe PDF file format

Pax Bellum ARID N18 Macroalgae Reactor - For Tanks 40-120 Gallons

Additional Info 2 available for download in Adobe PDF file format

Pax Bellum ARID N18 Macroalgae Reactor - For Tanks 40-120 Gallons

Additional Info 3 available for download in Adobe PDF file format

Pax Bellum ARID N18 Macroalgae Reactor - For Tanks 40-120 Gallons

Additional Info 4 available for download in Adobe PDF file format

Pax Bellum ARID N18 Macroalgae Reactor - For Tanks 40-120 Gallons

Additional Info 5 available for download in Adobe PDF file format
Ask a Question Earn 15 Points when you answer a question
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9 Questions
Displaying questions 1-9
This is rated for 40 gallons minimum, does that mean you wouldn't recommend using it on a 25 gallon system?
Asked : Jul 23, 2018
By : Mippy, Toronto Ontario
Thanks for your question. In a smaller system it will pull out too many nutrients which is why the rating is for a minimum 40 gallons. We have other algae scrubbers on our site such as Santa Monica which will suit your system volume.
Answered : Jul 24, 2018
By : Kat
What is the release date on the ARID?
What is the release date on the ARID?
Asked : Oct 11, 2017
By : Cody Barnes, Fort Myers, FL
Thank you for your question. We are all excited for the release of the reactors. The manufacturer has notified us that these reactors will be available approximately by mid to late October.
Answered : Oct 11, 2017
By : MD Tech

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