I have a 150p (150cm, and also about 150 gal empty!) rimless that I built a DIY stand for. I'll have a dedicated journal for this tank soon, as I've just taken down the previous iteration and installed a horizontal reactor into the stand.
This scape was taken down after a bit of a losing battle with algae, but man did I learn a lot about low-plant-mass scapes in high energy systems!
I will start a journal for the next iteration of this 150cm tank.
Here's the previous tank at it's "late summer" peak form:
I have it hooked up to my current favorite custom Oase Biomaster filter setup: Oase 2024/2025 Biomaster 850 Filter Head on a Biomaster 600 Canister and Prefilter setup, with drilled Pre-filter pipe for increased flow and no cavitation. The power of the 850, with the lower resistance of the 600 (and fits into my custom plywood stand!).
Will use this thread to share my experiences and thoughts! Please feel free to ask questions, as I feel like I'm one of the only people online I've seen purchase one of these, much less review one as well (so far).
First off, I have tried every form of CO2 injection under the sun.
On smaller tanks, in-tank diffusers are simple and get the job done with little fuss, so I run those.
On larger tanks (50 gallons and above) I have always had issues with CO2 injection.
If I used in-tank diffusers, they had to produce a TON of bubbles to reach a 1.0-1.2 pH drop (30ppm CO2).
If I used in-line diffusers, they worked better than in tank, but still produced a ton of "sprite water" and would eventually start working poorly after a few months. A few professionals I've spoken to believe that the ceramic body inside the in-line diffuser is a "consumable" part, and cleaning/eventual replacement is part of the tank's lifespan.
I tried the more common "vertical" spin-type CO2 reactor (also from Aqua Rocks), and while it was able to eventually reach a 1.0pH drop on my 55gal and did eliminate "sprite water", it would require a HUGE Co2 gas pocket built up through , made a ton of noise with the water vortex, and seriously slowed my Oase filter flow down quite noticeably, and gassed my fish a couple of times.
Enter: The Yugang Horizontal Reactor (forum post here)!
What a brilliant idea. Low maintenance, little flow impedance, NO noise, 100% CO2 dissolve rate, and built-in maximum adjustability (with reactors that have an off-center return/outlet). So so smart... I had to try it!
The basics are covered in the link above
I had to cut the built-in locked mounting plates so I could two 6" holes in the inner walls of my stand just to fit this design. I did it with a jigsaw (the acrylic is super easy to cut and sand into a smooth 6" diameter:
The one downside is it is really really HUGE. Besides my filters, this is the largest piece of equipment for the tank.The photos don't do it justice, this thing is massive. It's over two feet long with the outflow attachments, 4 inches in diameter at the acrylic tube, and the outer "plates" are just under 6 inches in diameter if you don't include the mounting plates.
It comes with "locked" mounting plates, but you can rotate the inflow/outflow plates by moving the blue screw holes by 1 screw in either direction. It's not a bad idea, but one of the main benefits of a horizontal reactor is the offset outflow (see left side above). On other horizontal reactor designs, you are able to rotate the outflow to adjust the CO2 pocket "overflow". This sets a maximum-sized CO2 pocket, which determines the max CO2 dissolve rate, and helps as a built-in safety feature to prevent gassing of your tank's inhabitants.
Honestly, I could have gone with the stainless steel version. I would have only needed to cut a 4" diameter hole in my stand's walls vs 6" (since the reactor is easily removed from the ring-mounting-clamps), and it freely rotates without "segmented" rotation like the default Acrylic reactor (meaning, before you saw off the acrylic mounting plates like I did).
However, you can't see what's going on inside the stainless steel reactors. That was the deciding factor for me between these reactors.
The first few days/weeks of using this reactor, being able to see inside has been amazing for troubleshooting, adjusting, and understanding what's going on.
However, now that I know how easy it is to set one of these up, and I have firsthand in-person experience seeing the mechanics with an acrylic reactor, I would consider a stainless steel reactor in the future.
How do you set one of these up?
Rotate the reactor until the top of the offset-outflow hole is just barely touching the level of CO2 pocket height you want to try:
Calculating if the Large (10cm diameter, 65cm body length) Horizontal Acrylic reactor from Aqua Rocks will work for my tank, and how to calculate it yourself:
I was skeptical that a reactor like this could really work for a tank of my size (about 120-130 gallons excluding hardscape, 150cm long and 60cm deep). But I did more research and found that this particular reactor is actually oversized for my tank! Which is good, because you can always reduce the rate of CO2 dissolution by simply rotating the reactor to raise the top of the internal outlet, as in my last comment.
The size of your reactor, and your reactor's gas-pocket-surface-area, should be determined by the area of your tank's surface area (since that's the only place for CO2 to gas out, it can't leave through the glass!). Yugang determined a rough ratio of 17:1 is the minimum tank:reactor surface area.
So, if the surface of my tank is 9,000cm2 (150x60cm), I would need a reactor with a maximum pocket-surface-area of ~530cm2 (9,000cm2/17ratio).
The Large acrylic horizontal reactor from ARC is 10cm in diameter, and 65cm in body length (only counting the length of the actual reactor tube dimensions). That means, at max reactor setting (see diagram above), this reactor has a max pocket-surface-area of 650cm2 (10x65cm).
That means I have a ratio of closer to 13:1 tank:reactor surface area, which is even more powerful than the minimum 17:1 tank:reactor.
Based off of these calculations, this reactor will work for tanks up to 180x60cm in surface area (like a standard 180p rimless), though it could also still supply plenty of CO2 to even larger tanks, just maybe not as quickly or as much as you'd like.
By the way, these dimensions for the acrylic reactor are the same for the stainless steel version, too.
A user here (sorry, I forgot your name and will update if I find you!) made this calculator to determine the minimum size of a reactor necessary for your tank:
Actual testing of the Horizontal Reactor
My supposedly accurate Hanna CO2 test kit is on backorder, so the most accurate way I have to measure my CO2 injection rate is through pH readings and the pH drop method. Read @Dennis Wong 's excellent article on measuring pH drop here. I also use glass drop checkers just to double check my findings.
Dissolved CO2 gas has a direct effect on lowering pH in our aquariums. There is also some relation with kH (a reading of carbonate hardness in your water). For most tanks between ~2-6kH, a 1.0pH drop equals about 30ppm CO2, which is high and ideal for growing plants, and my target for CO2 injection. I have extremely low KH tanks (between 0 and 1, I can't actually test it with the API test kits it's so dilute). With KH this low, you might need a 1.4 or 1.5 pH drop
The "Drop" is the difference measured between your CO2-injected tank water, and from a sample of your tank water that has been completely de-gassed of all dissolved CO2. You can degas a sample by leaving it out open-top on your counter for 24-48 hours, or through aggressive agitation (blending, stir plate, vigorous shaking).
Steps I took:
Set up reactor at about 2/3 full H2O to start (rotated until top of outlet was about 2/3 height of the inner reactor).
Took a sample of my aquarium water and put it on my stir plate with a stir bar for about 20 minutes, aggressively de-gassing my sample.
Calibrated my GHL Profilux aquarium computer and pH probe with ph4 and ph7 calibration fluids.
Measured the pH of my degassed sample after 30 minutes of stirring, then set up the probe in the aquarium.
Results:
The degassed sample reads about 6.8pH. I'm pretty skeptical of this, since this tank is FILLED with ADA Amazonia and driftwood. However, the probe reads the calibration fluids accurately, so I wonder if it has to do with my low KH and low GH? KH is <1, and GH is about 4-5 (100-130 ppm TDS). I'd expect a tank like this to be much lower, about 6.5, but I could be wrong? Either way...
The CO2 turns on at 7:30am and off at 4pm. Here are the first day's results:
Note that the tank had CO2 injection from the previous day still degassing. It would take days for a tank of this size, even with my very good surface agitation, to completely degas. With a very low KH, I think it's normal to have a ~1.0pH drop already before injection happens the next day (at least I hope!).
It took about 3 hours to reach my target 1.5ph drop (from degassed to injected). This isn't too bad with a tank of this size, but I was expecting better results. I also re-checked my degassed sample, both quickly with another 30 minute stir plate session AND I left my pH probe in the degassed sample for 11 hours all night, just to check. Yep, it's about 6.8ph (and clear that even 30 minutes of aggressive near-blending stirring is still not enough to fully degas your samples. You better shake them hard!). The lowest it dropped was about a 1.6pH drop, which should be plenty for my tank. Drop checkers were lime green at that point.
Day 2 showed similar results, 3 hours to a 1.5pH drop and a whopping 1.7pH drop at the 8 hour mark. Good, but I still want to reach that bottom level faster if possible just to see what it's capable of (the tank is only just planted, and I have no livestock inside). Let's increase the rate of CO2 by rotating the reactor to maximum strength (1/2 filled):
Now we're talking! The reactor reached a measured 1.5pH drop in only 2 hours on this huge tank, with tons of surface agitation. That's great!
But holy shit, a 1.75pH drop in 6 hours? That's absolutely going to kill my fish. So, while the curve got steeper quicker (and you can see that it really was able to bottom out much faster) it's going to likely be too much for my future inhabitants (drop checkers were slightly yellow at this point). I'm very curious to see what the Hanna test kit says about the ppm CO2 concentration here. Let's repeat another day:
Great results again, a steep curve that bottoms out at about a 1.7pH drop in 6 hours, with a ~1.5pH drop in 2 hours again.
My thoughts so far:
NO SPRITE WATER!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! I could scream my praises all day long. All you suckers saying "I don't mind the CO2 bubbles" have CLEARLY never seen crystal clear water through low-iron glass, where the only bubbles are from the plants pearling (I'm just joking, no one is a loser here). But seriously, having a method of CO2 injection that is this silent (it's VERY silent), doesn't impede my filter's flow, doesn't need cleaning like in-line diffusers, has a built-in safety in the overflow concept, is easily adjustable by simply rotating the reactor around slightly, AND keeps my water completely clear of CO2 bubbles is an absolute win. I genuinely think that many (if not most) of the world's future aquascaping galleries (Green Aqua, ADA, Liquid Nature, ADG, etc.) will be running horizontal reactors on their tanks.
It's annoying that the acrylic reactor from ARC has the super large 6" flanges on the sides, whereas the stainless steel reactor doesn't... but you can't see inside of it to quickly diagnose if something is wrong.
I think I'll likely end up setting my reactor to about 2/3rds full of water, and just starting it a few hours earlier, so the bulk of the peak of CO2 injection falls across the tank's photoperiod.
Please feel free to ask questions, request pictures, poke holes in my reasoning, or any other comments!
It's annoying that the acrylic reactor from ARC has the super large 6" flanges on the sides, whereas the stainless steel reactor doesn't... but you can't see inside of it to quickly diagnose if something is wrong.
I am kind of curious as to how seeing inside the reactor could diagnose something wrong. Pretty much, the water level has to be determined by the position of the outlet. So long as you are getting flow out of your outlet in the tank, and co2 is flowing and not leaking out somewhere,
I suppose it could help you set your co2 flow rate perhaps…
I am kind of curious as to how seeing inside the reactor could diagnose something wrong. Pretty much, the water level has to be determined by the position of the outlet. So long as you are getting flow out of your outlet in the tank, and co2 is flowing and not leaking out somewhere,
I suppose it could help you set your co2 flow rate perhaps…
I think the greatest benefit of a translucent/clear reactor is being able to determine if my CO2 injection is working properly or not with an instant glance. No pocket/minimal pocket? Something is wrong. Pocket set to the size I desire? All good! You can't do that with an opaque reactor, but that doesn't mean opaque is that much worse.
In an opaque (like the stainless) reactor, you're correct -- just rotate the reactor and increase CO2 until you see bubbles entering your aquarium through the overflow feature. This tells you you've maxed-out the CO2 pocket size relative to your outlet, so adjust your CO2 down until the overflow bubbles only occur every few minutes. With a stainless reactor, there is no way to tell that you're not maximizing CO2 efficiency without being able to see inside. This means that you have to run an opaque reactor in constant overflow mode, wasting CO2 and injecting semi-noisy bubbles into your tank, in order to know it's working properly. Not the end of the world, but you do lose any other functionality that could be provided from a clear reactor.
It's very easy to know when you're RIGHT at the level of your outflow with an opaque reactor because of the bubbles overflowing/entering your aquarium, but without a clear reactor there's no way to tell what actual level you have with anything below "overflow mode".
With a clear reactor like this, I can dial in my CO2 to fill my desired pocket size right before/on the brink of overflowing, so I'm not wasting ANY CO2 injection and have zero bubbles entering my aquarium, BUT I also still have the safety backup of the overflow should my solenoid break, my tank reach an end-of-tank-dump, or someone messes with my needle valve.
In reality, if you don't mind wasting a few bubbles of CO2 out of your lily pipe every few minutes, an opaque reactor won't bother you much, and will function just as well. Especially if CO2 is cheap near you (it's not near me!), you shouldn't mind at all, and the overflow bubbles will be enough to "show you" that your reactor is still working.
All I can say is after hands-on use for the last month or so, I think I'll always prefer a translucent/clear reactor over an opaque one, if possible.
Same here. It’s not outrageous, but it’s not an expense I like. A 20lb tank gives me a lot more time in between fill ups but I prefer to ration it as best I can with precision instead of wasting it. I wana make one of these soon
Thank you for sharing this experience. I almost pulled the trigger on the sale they had last fall. I decided not to get it for the sole reason that the size was a problem for my setup.
Thank you for sharing this experience. I almost pulled the trigger on the sale they had last fall. I decided not to get it for the sole reason that the size was a problem for my setup.
Yes, I still think simple in tank or in-line diffusers work for smaller setups and setups with less cabinet/behind-the-tank space. For larger tanks, I have a feeling this kind of reactor will be considered the best choice.
Welcome to ScapeCrunch @Naturescapes_Rocco , and thank you for doing this review.
Overall I concur with your observations, but allow me to add a few comments:
I agree that both transparent and opaque work. For the opaque one can just use a bubble counter, and as CO2 cannot disappear one can assume that CO2 that's gets injected will be absorbed in the aquarium water. So there is no real need to observe the gas pocket.
When I do have the ability to see the gas pocket, the main benefit that I use is for checking how much gas remains after CO2 is shut off. This is a measure for the purging in overflow mode and helps me to keep CO2 injection stable at minimum CO2 losses (like 10-15%)
Using a pH/CO2 controller for CO2 injection and stability
Using a precision CO2 regulator to precisely adjust CO2 injection
Overflow mode.
Most current users are either using a pH/CO2 controller or a precision CO2 regulator. There will be a reservoir of almost pure CO2 gas in the reactor, and the physics/chemistry of CO2 absorption into the water will be similar to any other reactor that may or may not use CO2 bubbles. As is also the case in bubble reactors, gradually we...
I am a big fan of overflow mode to stabilise my CO2 injection, with minimal losses of CO2. When I see a few small bubbles escape into the tank every minute or so, I know it is all good. As a final check, for a transparent reactor, I may observe the remaining gas at the end of the day but this is not a necessity.
With regard to the size I calculated that it will be nearly impossible to pack as much power in a bubble reactor, as compared to a horizontal reactor the same size. However, as you say, reactors are more often used on larger tanks, while diffusers more often on smaller tanks. This is the reason that AquaRocksColorado prioritised larger tanks initially, hence bigger reactors. There is really no reason why the reactor can't be minimised, even to the size of a matchbox with a dosing pump pushing some water through. I have done experiments with smaller reactors, where I also integrated the bypass function into a very small form factor, smaller but much more powerfull than a bubble reactor
Finally I got also overflow mode to work, and the solution is really simple to replicate for other users.
In summary
This reactor pushes around 1.2 pH drop on a 50 gallon tank
Can be used with precision regulator, pH controller, or in overflow mode for which the reactor geometry stabilises CO2.
Can easily handle the flow of FX4 (2650 l/hour), no external bypass needed.
Costs of parts about 6 USD altogether, and with some experience can be built in 30 minutes.
500 ml box, 7 inches long. As...
When I was learning how a horizontal reactor works, and step by step clarifying the physics and operation, having a transparent prototype reactor was a big help, if not essential. Now that I figured it out, the ability to observe it is a nice to have but not a necessity. If there are any remaining issues that were not covered in my thread, I can help to clarify and explain why the transparency is not required.
Very cool this is almost a journal already! Looking forward to seeing how it grows out.
Thank you Rocco for this detailed real-life review! This kind of walkthrough is super helpful for new readers looking to figure out exactly how this weird looking horizontal thing from Aqua Rocks will help them manage CO2 injection in their own tanks
My problem with these reactors is that i use ro water exclusively and they leach. I really need high grade stainless steel or glass. As a simple example leaving water in a python hose for a few days and raise the ec from 10 to 1000.
Been testing for about a month and a half on my new 150cm (about 150 gal) scape to great success! In fact, a little TOO much success.
I purchased a Hanna Co2 Test Kit to use with my 4dkH Drop checker and the pH drop method, to determine CO2 injection rate and amount. I found that I needed to run the reactor with less power. The reactor needs to be set to about 3/5th full of water (2/5th full of CO2) to get 30ppm CO2 in my tank easily. I also run a lot of surface agitation which is really important for oxygen and CO2 off-gassing.
At full power (1/2 full gas), it took VERY little time to hit 1.0pH drop (compared to degassed sample), less than an hour to hit 1.5pH drop, and less than 2 hours to hit a 1.75pH drop. I found that the Hanna test kit was showing 40-47ppm CO2 at full strength! Way too much for livestock, so I reduced the power.
However, note that reducing the power also reduces the speed of which CO2 is injected/reaches equilibrium between injection and off-gassing.
That's not a problem, just turn on the CO2 earlier in the day!
I like my CO2 to have almost reached equilibrium before the lights even come on. I measure this with my GHL pH probe as seen above. I found that if I set the CO2 to start 2-3 hours before the lights come on, I'm at 95% equilibrium and the plants have ample CO2 for the entire day. I also have the CO2 turn off 2 hours before the lights do, since there is so much CO2 dissolved in the water itself:
If I was using a diffuser, turning it off 1 hour before lights turn off would probably be just fine.
During the photoperiod, I can test the water and see the results are between 25-30ppm the entire time. The plants are PEARLING LIKE CRAZY. I've never had so much oxygen like this before coming off of the plants themselves... I didn't want "CO2 sprite water" with a CO2 diffuser, but here I am with "Oxygen sprite water"!
I will note that my shrimp do NOT like this. I always thought amano shrimp were fine at 30ppm CO2, but man do they hang as close to the surface as they can during the day... All the other fish (rainbow shiners, white clouds, SAEs, Garras) are totally fine, though the new Otocinclus seem to also stay at the surface during CO2 injection. Hopefully they adjust.
I think this will be the last horizontal-reactor-specific update in this post, since it's about time I start my first Journal for this tank in a separate thread! Let me know if you have any thoughts or questions.
Can you clarify this for me? It was my understanding that every .25 drop in pH doubles the concentration of CO2 in the water. So if a 1 pH drop is 30 ppm CO2, a 1.25 drop would equal 60 ppm CO2, and a 1.5 drop would equal 120 ppm CO2. Since the reactor is meant to achieve a 1.5 pH drop, and lots of people are using it that way, I figured 120 ppm should be okay as long as the fish aren’t showing any distress. This is assuming that the pH drop is measured from the true de-gassed baseline. I have mine set lower than max, so my Hanna checker shows a CO2 concentration of 60 ppm , and the fish aren’t having any problem with that. I haven’t measured the pH drop though, because my pen broke and I trust the reactor in overflow mode. Does all this make sense, or have I not understood something?
In normal non-Injected aquariums, CO2 is about 3ppm. Since pH is logarithmic (base x10), 1.0pH drop equates to a 10x increase, or 30ppm CO2.
A 1.5pH drop would be 45ppm. However, this is all at 2-16 kH (because kH has a direct effect on pH).
In my tanks with zero kH, a 1.0pH drop might only equate to ~20-25ppm CO2. That's why a pH drop of 1.75 might only be ~45ppm CO2 for me, because of a low-kH environment.
Either way, to be honest there is NO way you're injecting 120ppm CO2 lol. Most livestock will go comatose between 40-50ppm, depending on dissolved oxygen (which is independent from dissolved CO2).
Okay, math is not my strong suit, lol! I guess I either misunderstood what I read previously, or misremembered. When I did the Hanna test on my tank previously, the tank was at 0-1 kH, and I read the Hanna test at 90, but I quite possibly had user error on the Hanna test.
Since then I’ve been bringing the kH up to 3, and that’s what it reads today. I did the Hanna test again today. It starts to go pink at .4 titrant injected, and stays pink at .5 titrant injected. Would you say that’s 40 or 50 ppm CO2? The CO2 drop checker stays an olive green verging on yellow these days.
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