Description
GLA PRO-CO2 Atomizing Reactor 5L
The GLA PRO-CO2 Atomizing Reactor 5L combines ultra-fine ceramic CO2 atomization with a large external dissolution chamber to improve CO2 utilization and reduce gas accumulation in planted aquarium systems.
Unlike conventional reactors that primarily rely on waterflow and contact time to dissolve larger gas bubbles, the PRO-CO2 Reactor first atomizes CO2 into a fine mist. The reactor chamber then provides additional contact time for dissolution before water returns to the aquarium.
The result is efficient CO2 delivery with reduced visible microbubbles, less gas pocketing, and no in-tank diffuser required.
At a Glance
- Reactor Design: 5-liter hybrid ceramic atomizing reactor
- Installation: External filter return line
- Typical Working Pressure: Approximately 20–25 PSI
- Recommended Waterflow: Minimum approximately 300 GPH; typical operating range 400–1200 GPH+
- Included Adapters: 12mm, 16mm, 20mm, and 1"
- Dimensions: Approximately 20" tall × 6" diameter
- Construction: Clear acrylic chamber with enlarged internal flow path
- CO2 Connection: Push-connect fitting
- Maintenance: Removable, replaceable ceramic atomizer
- Power: No separate electrical connection required for the reactor
Best For
- Planted aquariums using compatible external filtration or return pumps
- Aquarists seeking efficient CO2 dissolution with less visible mist inside the aquarium
- Medium to large planted aquariums and higher-demand CO2 installations with adequate filtration flow
- Aquarium installations where an in-tank diffuser is not preferred
- High-flow filtration systems requiring flexible tubing adapters and a serviceable reactor design
The reactor's suitability depends primarily on available waterflow, plumbing compatibility, and CO2 demand rather than aquarium size alone.
Beyond Conventional CO2 Reactors
Innovative Engineering. Exceptional CO2 Dissolution.
The GLA PRO-CO2 Atomizing Reactor 5L represents a different approach to aquarium CO2 delivery. Rather than simply introducing gas into a chamber and relying on waterflow to dissolve it, GLA combines two complementary technologies: ultra-fine ceramic atomization and high-capacity reactor dissolution. The result is a sophisticated hybrid system engineered to make more effective use of every bubble of CO2.
What makes this reactor different is how its components work together. A precision ceramic atomizer breaks CO2 into an exceptionally fine mist before it enters the spacious 5-liter dissolution chamber. This dramatically increases the surface area available for gas exchange, helping CO2 dissolve efficiently while reducing the gas accumulation, visible microbubbles, and wasted injection associated with less efficient systems.
Innovation extends beyond the atomizer. An enlarged internal flow path supports powerful filtration systems, while the removable ceramic assembly, replaceable components, and versatile connection options make the reactor practical to maintain and adaptable to different installations. Every major feature has a purpose: better CO2 utilization, efficient water movement, straightforward servicing, and dependable long-term operation.
For aquarists who invest in quality lighting, filtration, and fertilization, CO2 delivery deserves the same attention. The PRO-CO2 Atomizing Reactor is more than an alternative to a conventional diffuser or reactor. It's an investment in a thoughtfully engineered CO2 delivery system designed to bring greater efficiency, refinement, and control to the planted aquarium.
Filter Compatibility & Installation
The GLA PRO-CO2 Reactor installs externally on the return line of a compatible canister filter or dedicated circulation system. It must receive adequate waterflow to operate effectively.
Correct Installation: Canister Filter → PRO-CO2 Reactor → Aquarium Return
Important: Install the reactor on the filter return line only. Do not install it on the filter intake line.
The included 12mm, 16mm, 20mm, and 1" adapter sets accommodate a variety of filtration connections, including many Fluval FX Series installations when the appropriate fittings are used.
Confirm your actual tubing and connection dimensions before installation. Each adapter must be fitted with its matching silicone O-ring to provide a proper water-tight seal.
Allow sufficient cabinet space for the reactor's height, plumbing, and maintenance access.
Initial Setup & Priming
Proper installation and priming are important for removing trapped air and establishing normal water circulation through the reactor. The chamber must be completely filled with water before CO2 injection begins.
- Select the Correct Adapters: Choose the included adapter size appropriate for your filtration system. Confirm that the matching clear silicone O-rings are properly seated beneath the adapters.
- Install the Reactor: With filtration turned off, connect the reactor to the filter return line. Connect the filter outflow to the reactor water inlet and the reactor outlet to the aquarium return line.
- Connect the CO2 Supply: Insert CO2-resistant tubing fully into the push-connect fitting on top of the reactor. Install a compatible check valve between the regulator and reactor. Keep CO2 injection turned off during priming.
- Prepare for Priming: With filtration still off, loosen one reactor lid screw approximately one to two turns. Do not remove the screw. Place a towel beneath the reactor to collect water released during priming.
- Fill and Vent the Reactor: Start the filtration system and allow the chamber to fill with water. Trapped air will escape through the loosened screw location.
- Complete Priming: Continue until water begins to flow from the loosened screw location. Allow a small amount of water to overflow to help remove remaining air, then hand-tighten the screw. Keep escaping water away from electrical equipment.
- Inspect for Leaks: Check the reactor lid, adapters, tubing connections, and fittings. Confirm the chamber is filled and all connections are secure before beginning CO2 injection.
- Begin CO2 Injection: Set the regulator to the appropriate working pressure, typically 20–25 PSI for GLA PRO-CO2 reactors. Begin with a conservative CO2 flow rate and make gradual adjustments according to aquarium conditions.
Important: Reactor lid screws are designed for hand tightening only. Never use screwdrivers, drills, pliers, power tools, or excessive force. Overtightening can damage the screws, threads, O-rings, or acrylic components.
Lid Screw Precaution: The reactor lid screws are designed for hand tightening only. Do not use screwdrivers, drills, pliers, or excessive force. Overtightening can damage the screws, threads, seals, or acrylic components.
Working Pressure, Waterflow & CO2 Adjustment
GLA PRO-CO2 reactors, including standard and atomizing configurations, typically operate at approximately 20–25 PSI. Actual settings may vary according to the installation and operating conditions.
The reactor has a recommended minimum waterflow of approximately 300 GPH, with a typical operating range of 400–1200 GPH or greater. Actual waterflow through a filter can be lower than its advertised pump rating due to tubing, filter media, plumbing, and installation resistance.
Working pressure and CO2 injection rate are separate adjustments. Set sufficient working pressure for atomizer operation, then use the regulator's precision needle valve to control the amount of CO2 being injected.
When switching from another diffuser or reactor, begin with a conservative bubble rate. More efficient dissolution can change the amount of CO2 available to the aquarium even when the bubble count remains the same.
Make gradual adjustments while monitoring your drop checker, aquarium circulation, and livestock. A drop checker responds with a delay and should not be treated as a real-time safety indicator.
For more information, see our CO2 Working Pressure & Flow Guide.
Cleaning & Maintenance
The removable ceramic atomizer allows routine cleaning and replacement without requiring a new reactor assembly.
Over time, algae, biofilm, or mineral deposits may restrict the ceramic membrane and reduce fine-bubble production. Clean the atomizer using methods appropriate for its materials and follow the supplied maintenance instructions.
During maintenance, also inspect:
- Ceramic atomizer condition
- Internal standpipe and flow passages
- Lid seal and adapter O-rings
- Tubing connections and fittings
- Acrylic chamber and lid for damage
Always stop CO2 injection, isolate the water circulation, and relieve any remaining pressure before opening or servicing the reactor.
After reassembly, restore waterflow, prime the reactor as needed, and inspect all connections for leaks before resuming normal operation.
Specifications
- Model: GLA PRO-CO2 Atomizing Reactor 5L
- Reactor Chamber Capacity: 5 Liters
- Construction: Acrylic
- Height: Approximately 20"
- Diameter: Approximately 6"
- Diffusion Technology: Removable ceramic atomizer with external dissolution chamber
- Working Pressure: Typically 20–25 PSI
- Minimum Recommended Waterflow: Approximately 300 GPH
- Typical Operating Flow: 400–1200 GPH+
- Installation: External filter return line
- CO2 Connection: Push-connect fitting
- Included Adapter Sizes: 12mm, 16mm, 20mm, and 1"
- Additional Power: Not required when operated using an existing compatible filtration system
What's Included
- GLA PRO-CO2 Atomizing Reactor 5L
- Installed removable ceramic atomizer
- 12mm adapter set
- 16mm adapter set
- 20mm adapter set
- 1" adapter set
- Matching clear silicone O-rings
- Installation and maintenance guide
Required Separately: A compatible pressurized CO2 system, CO2-resistant tubing, and an external filter or circulation pump capable of providing sufficient waterflow. A compatible CO2 check valve is recommended and sold separately.
Frequently Asked Questions
How does this reactor differ from a conventional CO2 reactor? The PRO-CO2 Atomizing Reactor uses a ceramic membrane to create fine CO2 bubbles before they enter the dissolution chamber. This increases gas-to-water contact and helps improve dissolution compared with conventional large-bubble reactor designs.
Will I still need an in-tank CO2 diffuser? No. The reactor introduces CO2 externally through the filter return line, so a separate in-tank diffuser is not required.
Will I see CO2 bubbles in the aquarium? The reactor is designed to reduce undissolved CO2 and visible mist. Some microbubbles may still be present depending on waterflow, CO2 injection rate, and system configuration.
Does the reactor eliminate gas accumulation? The hybrid atomizing design helps reduce gas pocketing, but small amounts of gas may still accumulate under certain operating conditions. Persistent gas pockets may indicate insufficient waterflow, excessive CO2 injection, or trapped air requiring attention.
Is the reactor compatible with Fluval FX Series filters? The included 1" adapter set supports many Fluval FX Series installations. Confirm the specific filter's tubing and connection dimensions before ordering.
Can I clean or replace the ceramic atomizer? Yes. The atomizer is removable for cleaning, inspection, and replacement. The entire reactor does not need to be replaced for routine atomizer servicing.
Does the reactor require an additional pump? Not when your existing compatible filtration system provides adequate waterflow. The reactor does not contain a motor or require its own electrical connection.
Is a CO2 check valve included? No. A compatible check valve is recommended to help prevent water backflow toward the CO2 regulator and is sold separately.
Pre-Sales & Shipping Information
GLA CO2 reactors are non-returnable. For questions about filter compatibility, tubing adapters, installation, or reactor operation, please contact GLA before purchasing.
Customer Reviews
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Works exactly like you want it too.
This is my first reactor so I have no experience with other types. However I did do my homework and asked a billion questions on Redit and forums regarding other reactors. I created a spreadsheet of all data ? and everything brought me to this new style reactor. I’m very pleased with the quality and functionality. GLA was very helpful at guiding me along the way. Strongly recommend this unit.
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Whatever co2 reactor you use, throw it away.
Yugang was a nightmare to deal with all the time and was wasteful with Co2. I hated how stupid huge it was taking up the length of the cabinet. Constant fiddling and adjusting and it just isn’t a system fit for everybody. This month I switched to GLA reactor and the difference is incredible. While it may be a tall unit, it doesn’t take up so much space lengthwise. It also doesn’t require any messing with or constant adjusting of the co2 system. I set it up and it worked instantly. My ppm of 40/45ppn is steady all day confirmed by my co2 test kit and GLA new 4DKH solution. I like that there is no gas pocket at any point of the day. Co2 dissolving quickly which is just astounding. The atomizer I noticed is removable so I like that and I’m waiting for GLA to provide the atomizers as a separate purchase so I can swap between cleanings. The atomizers itself creates a super fine mist where the bubble is so small it dissolves in 2-3 seconds. The surface area is immense so your levels of co2 are rock solid so I advise to go slow as I almost gassed my tank, so my advice is to start slow on co2. I made that mistake because I forgot to adjust my co2 from previous reactor. Otherwise absolutely awesome reactor. But please, GLA provide us with the option to buy an extra atomizer as we could really use them. ?
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This is the best reactor.
I own several reactor types over the years and this one is by far the very best I’ve ever used. It waste no co2 and is always full of water. No bubble inside at all even at the end of the photoperiod. There is truly nothing else like it anywhere. Just know the unit is quite large so confirm you have space. GLA is always providing game changing CO2 equipment and I’ve been a customer for a few decades now. High quality from top to bottom and includes all these extra fittings for various tube sizes.
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Total game changing CO2 reactor.
Coming from my first Cerges reactor to then the nightmare Yugang reactor and back to a Cerges. I ended the nightmare by giving the GLA reactor a shot. First thing I noticed is its massive size, an absolute monster of a reactor. Literally I set it up and off the start it just started working like you would want a reactor to perform. In 55 minutes or less my ph was down 1.2 points and a lime green drop checker after my first hour. At 3hrs was near gassing my fish so I had to make some adjustments to surface agitation. I made no adjustments to co2 into the reactor. Now it’s absolutely perfect. I feed co2 9hrs of the day. No big gas bubble, no sounds. And most of all no waste of CO2 like that dang nightmare Yugang reactor which was a total abortion. If you are looking to go with a CO2 reactor this is the only one you get. GLA killed it with that huge atomizer in the reactor. Love it!
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Took the plunge on this and what a game changer.
This thing is quite large and very high quality. The diffusion and saturation of CO2 is phenomenal. Totally worth the investment GLA has knocked it out of the park once again. I absolutely love this reactor. Comes with every size tubing connector imaginable and the diffuser is easily removable. Best reactor you’ll find is this. I had the Yugang style reactor and what a total abomination and waste of money and CO2. I don’t know why people think a reactor burping huge bubbles of co2 is ideal lol what a total junk concept. Buy this instead safe the hassle.
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Where has this been all my years in aquascaping.
19 years aquascaping where I’ve used reactors and diffusers of so many types. My previous reactor was a Yugang reactor which was at first I thought I good system. Bloody hell that was a disaster. It waste so much CO2 and it does it by design which to me is insane. So I went back to GLA diffusers like I’ve always used because they always have the best diffusers. They work so well in fact it creates an absolute fog mist of CO2. I grow tired of the constant fog so I decided to try this new reactor from GLA. People, when I say this thing is the best I don’t say that lightly, it works tremendously well and doesn’t waste a drop of CO2. GLA deserves an award for constantly bringing the newest and best innovations to planted tanks. From the CO2 regulator they invented to the high pressure atomizers and now this animal. It’s an absolute beast of working functional co2 delivery I can count on day after day. Thank you GLA Team for answering all my questions and supporting the hobby that brings me much joy.
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The Rolls-Royce of aquarium CO₂ reactors
The CO₂ Reactor is the Rolls-Royce of aquarium reactors. From the moment you open the box, it's clear this is a premium, expertly engineered product. The craftsmanship is outstanding, and every component feels solid and built to last. Just as impressive as the reactor itself is the company behind it. Their customer support is exceptional—they genuinely care about their customers and stand behind their products. That level of service is becoming rare these days. While it costs more than many other reactors, you truly get what you pay for. If you want a high-quality CO₂ reactor that performs flawlessly and is built to last, this is the one. It's worth every penny and is the real deal.
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Gla pro
Great reactor
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Serious piece of kit
This thing is fantastic. So well built and it feels like it will last forever. Running in an 88g Fluval Siena and no more bubbles. Not the least expensive option to be sure, but worth every penny IMO. Just make sure you have a filter with some power and you won't be disappointed at all. Well done GLA!
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No question this is the best CO2 diffusion ⭐️⭐️⭐️⭐️⭐️system on earth.
My second reactor so I have good experience using reactors. First, be smart, start your bubble rate slow because this baby works so well your fish and equipment will start pearling. Not just plants, but the hardscape, glass pipes and anything else in the tank. I was very close to gassing my fish at my usual bubble rate, luckily I noticed and dropped my bubble rate down to half. This thing is absolutely brilliant, it works incredibly well so I advise you start slow and watch your drop checker. The atomizer inside is unreal, it pulverizes co2 into a very fine atomized mist like no other diffuser I’ve seen. I have a feeling I’m going to finally start saving lots of co2. Kudos to the team at GLA for bringing yet another pioneering CO2 device to the hobby. You guys are do a couple of rewards for this CO2 reactor and modular manifold system. ⭐️⭐️⭐️⭐️⭐️
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CO2 Reactor and Support
I was a complete newbie at this and their texting support was just friggin AMAZING at helping me set it up and even provided reference images! It works fantastically and I've had ZERO issues!
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Without doubt the best co2 reactor in the game.
This is a huge reactor so be sure to read the specs. I suggest adding 2” to what they list due to the hose connections. It’s a large volume unit where zero co2 escapes, zero waste! My tank is on point daily with co2. Plants pearling and my plumbing looks rad!
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Best co2 reactor on the market.
I’m not novice to using co2 reactors as I’ve got a few I’ve used. This GLA reactor is near perfect. I’d rate it 5 stars if it came with a check valve for the co2 tubing. Other than that it’s perfect. Very well made design without a drop of co2 escaping. I have mine hooked up to a dedicated pump made by Iwaki and it moves water like a beast at 1800gph. Reactor performs perfectly everyday.
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Absolute CO2 excellence.
I own quite a bit of equipment from GLA and every time it’s top quality stuff. Their service is also unmatched. I’m louding service because they have an incredible text message service. They provide photos and videos of whatever you might need. Really great people to work with. But back to this reactor, it’s a really good reactor. Comes with a bunch of hose fittings to choose from and they even include a whole dang roll of Teflon tape lol. It took me about two days to dial in to perfection. Tank is crystal clear and void of the 7-Up look from traditional diffusers. Now the only visible bubbles are my plants peeling like mad.
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Outstanding reactor and premium customer service.
The reactir is absolutely outstanding and GLA’s customer service is amazing. They should write a book on how to setup and install co2 systems on very large tanks. My tank is 230g in size and they helped me from start to finish and I could not be more pleased. Everything was shipped for free. The service was free and worth every penny in my investment in a full GLA CO2 system. Everything works like a top. Thank you GLA.
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It’s an absolute unit of a co2 reactor.
You really don’t get the size of how big it is until it arrives, it’s huge! Pro tip: I installed the GLA inline at the top to atomize co2 prior to it entering the reactor and it works INCREDIBLY well. Then! I used the original co2 inlet port for my GLA Nectar AIO Dosing port. Injecting fertilizer into a virtual mixing vessel prior to entering the tank. This was GLA’s advice and I could not be happier. What a work of art this system has turned out to be.
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GLA is the best in aquascaping gear.
Been a customer with GLA since 2008. Still using my old co2 kit from then and now upgraded to this co2 reactor. It’s been an amazing unit and works really well on my 120g tank. It’s a huge reactor so it’s been able to handle the high flow from my pump and large amount of co2. Thanks GLA for continuing to put out great products.
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Very pleased with this co2 reactor.
Super efficient and high quality reactor. Using this on my 90g has been an absolute success. Plants are happy and my drop checker is a perfect shade of green/yellow. Yes I keep my co2 on the high side but my tank is happy!
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Beast mode has been activated!
The photo does no justice with this reactor. It’s massive and works perfectly! Co2 levels are stable and stay steady everyday. I have my co2 on a ph controller so my levels are dialed into perfection. High quality unit that freaking works! A++
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This thing rocks!
This is what I’ve wanted since ditching my Cerges reactor. That thing was a nightmare and an absolute abortion of a design. With this it’s just super easy to use and I don’t ever mess with it. My co2 is stable and always puts my drop checker near the yellow zone in short time.
