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CO2 Spray Bar

Yugang

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13 Mar 2021
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336
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Hong Kong
The fancy term ‘CO2 reactor’ suggest something magical is going on, but essentially it is a tube filled with water and bubbles, where the surface area of the bubbles drives the absorption of CO2 gas in the flow of water.
My own CO2 reactor (modified Aquamedic with bypass) has been working perfectly for several years and was not worth spending any more time on. Well, until recently, when I took pictures and estimated the surface area of CO2 bubbles and came to some new insights.

I have been experimenting with a new CO2 setup, that I would call “CO2 spray bar”.
It works so well, that I am not sure if I will use my reactor again (I have given up on CO2 diffusors long time ago).

1653377734461.png



The full length of my tank has a spray bar for filter water return, that creates a gentle surface flow to the front with some surface agitation. The water then goes down and returns via the bottom to the back again and then upwards.
The CO2 spray bar is a half-pipe over the full tank length, filled with CO2. It is open at the bottom where it creates an absorption surface to the water flow. Mounted just below the spray bar is the CO2 bubble source, so that bubbles float up and replenish the reservoir in the spray bar.
Absorption at the open bottom of the CO2 spray bar enriches the waterflow, which goes straight down to the plants, homogeneous over the full length of the tank.

Benefits
  • No need for CO2 reactor (expensive, slows filter flow), or diffusors (stability, maintenance).
  • No need for expensive precision regulator. The CO2 absorption is proportional to the surface area of the CO2 spray bar, which is constant when entirely filled with gas. The regulator has no role, other than supplying just enough CO2 to keep the spray bar full. Set regulator 10% exceeding CO2 absorption, so that once a while an excess bubble escapes from the reservoir yet keeps it fully filled
  • Safe for life stock. When too much CO2 is injected, the spray bar will overflow and release bubbles to surface of tank. pH/CO2 ppm is not affected at all.
  • Cheap. Just some plastic parts and glue.
  • Can be used with pH controller as well. The inherent safety of the CO2 spray bar mitigates several risks associated with pH control. Benefit is that a pH controller allows fast ramp up, and mitigates the impact of variations in surface agitation.

Full tank shot. As I used transparent plastic for both spray bars, at water surface, the CO2 spray bar is hardly visible.

1653377856634.png


Top and bottom shots of CO2 Spray Bar

1653377902091.png
1653377916975.png


Performance

1653377952264.png
1653377973842.png


pH stable within 0.1 between 10:00 AM and 14:00, when CO2 is switched off. 14:15 CO2 Spray Bar half empty, and pH starts to rise again. Drop checker lime green and plants pearling. Fish happy.

Design rules / estimation
For my tank (100 * 45 * 60 cm) I use a 1 inch, 90 cm long CO2 spray bar This is 216 cm2 surface area. The ratio between tank surface area (4500 cm2) and CO2 spray bar (216) is 20.8 :1. For other tank dimensions, this ratio is a good approximation how to find the optimal dimensions of the spray bar.

Notes:
  • Still contemplating another concept, that will be outperforming dream machine, not to mention traditional CO2 controllers. Perhaps it is best to collect some more data on CO2 spray bar to better understand if a more technology heavy approach makes any sense at all. Still excited about the other concept though, may introduce that later.
  • Hope that others can verify the CO2 spray bar concept in their tanks, and post data on this thread, as I can still hardly believe my observations and the strengths of such a simplistic concept. It will also help validate the concept for different tank sizes, water flows and planting.
Hope you all enjoy, and perhaps build one yourself :)
 

Ria95

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11 Aug 2021
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DE
Thanks for sharing. The build looks clean. The description essentially sounds like a passive CO2 diffusor.

It might be worth considering adding a degas valve at the top like some of the bell diffusers have to let out from time to time the "air" at equilibirum with the tank. This can accumulate over time and reduce the efficiency.
 

KirstyF

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25 Jul 2021
Messages
468
Location
Kidderminster
The fancy term ‘CO2 reactor’ suggest something magical is going on, but essentially it is a tube filled with water and bubbles, where the surface area of the bubbles drives the absorption of CO2 gas in the flow of water.
My own CO2 reactor (modified Aquamedic with bypass) has been working perfectly for several years and was not worth spending any more time on. Well, until recently, when I took pictures and estimated the surface area of CO2 bubbles and came to some new insights.

I have been experimenting with a new CO2 setup, that I would call “CO2 spray bar”.
It works so well, that I am not sure if I will use my reactor again (I have given up on CO2 diffusors long time ago).

View attachment 189051


The full length of my tank has a spray bar for filter water return, that creates a gentle surface flow to the front with some surface agitation. The water then goes down and returns via the bottom to the back again and then upwards.
The CO2 spray bar is a half-pipe over the full tank length, filled with CO2. It is open at the bottom where it creates an absorption surface to the water flow. Mounted just below the spray bar is the CO2 bubble source, so that bubbles float up and replenish the reservoir in the spray bar.
Absorption at the open bottom of the CO2 spray bar enriches the waterflow, which goes straight down to the plants, homogeneous over the full length of the tank.

Benefits
  • No need for CO2 reactor (expensive, slows filter flow), or diffusors (stability, maintenance).
  • No need for expensive precision regulator. The CO2 absorption is proportional to the surface area of the CO2 spray bar, which is constant when entirely filled with gas. The regulator has no role, other than supplying just enough CO2 to keep the spray bar full. Set regulator 10% exceeding CO2 absorption, so that once a while an excess bubble escapes from the reservoir yet keeps it fully filled
  • Safe for life stock. When too much CO2 is injected, the spray bar will overflow and release bubbles to surface of tank. pH/CO2 ppm is not affected at all.
  • Cheap. Just some plastic parts and glue.
  • Can be used with pH controller as well. The inherent safety of the CO2 spray bar mitigates several risks associated with pH control. Benefit is that a pH controller allows fast ramp up, and mitigates the impact of variations in surface agitation.

Full tank shot. As I used transparent plastic for both spray bars, at water surface, the CO2 spray bar is hardly visible.

View attachment 189052

Top and bottom shots of CO2 Spray Bar

View attachment 189053View attachment 189054

Performance

View attachment 189055View attachment 189056

pH stable within 0.1 between 10:00 AM and 14:00, when CO2 is switched off. 14:15 CO2 Spray Bar half empty, and pH starts to rise again. Drop checker lime green and plants pearling. Fish happy.

Design rules / estimation
For my tank (100 * 45 * 60 cm) I use a 1 inch, 90 cm long CO2 spray bar This is 216 cm2 surface area. The ratio between tank surface area (4500 cm2) and CO2 spray bar (216) is 20.8 :1. For other tank dimensions, this ratio is a good approximation how to find the optimal dimensions of the spray bar.

Notes:
  • Still contemplating another concept, that will be outperforming dream machine, not to mention traditional CO2 controllers. Perhaps it is best to collect some more data on CO2 spray bar to better understand if a more technology heavy approach makes any sense at all. Still excited about the other concept though, may introduce that later.
  • Hope that others can verify the CO2 spray bar concept in their tanks, and post data on this thread, as I can still hardly believe my observations and the strengths of such a simplistic concept. It will also help validate the concept for different tank sizes, water flows and planting.
Hope you all enjoy, and perhaps build one yourself :)

Interesting concept @Yugang.

I note ur PH drop goes as high as 1.6. Have you played with sizes of the Co2 ‘spraybar’ tubing at all, to achieve lower levels? (As many fish keepers like to keep inside the 1ph level for safety)

Also, my understanding (and correct me if I’m wrong) is that the quantity of Co2 being delivered to/absorbed by the water will be directly related to the surface area made available by the tubing size and therefore adjustment of the Co2 level could only be achieved by changing the pipe size!!?

If so then alternatively, if you utilised a triangular shaped pipe, the Co2 surface area and subsequently the absorption level would increase/decrease depending on how full that pipe was, would it not? This would still require the ability to either finely tune delivery of the Co2 to maintain a very specific level (potentially defeats the object of some of your benefits) or some sort of adjustable overflow that could be set to allow excess Co2 to escape at a particular point? Don’t think that would be too tough to engineer!

Just thoughts really but I feel maintaining the ability to easily adjust the Co2 level would be a ‘must have’ for a lot of folks!
 

Yugang

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It might be worth considering adding a degas valve at the top like some of the bell diffusers have to let out from time to time the "air" at equilibirum with the tank. This can accumulate over time and reduce the efficiency.
Perhaps, but I suggest to wait for further user experience and see if indeed efficiency is significantly reduced (in my experience, no problem here). Degassing the CO2 spray bar is as easy as rotating it 90 degrees and back, which I do at weekly water change anyway :)

I note ur PH drop goes as high as 1.6. Have you played with sizes of the Co2 ‘spraybar’ tubing at all, to achieve lower levels? (As many fish keepers like to keep inside the 1ph level for safety)
Yes, I built several prototypes, each at 40 HKD (4 GBP) materials cost. Some shorter, some longer, all with different pH drop result. .
I used this 1.6 drop in my posting as a proof of concept, indeed a slightly shorter bar may give a safer 1 pH drop for the average user and tank setup.
Although it is not beginners advice, several users (@GreggZ pH 1.4 drop ) are higher. In my tank the Rasbora's first give warning signs (while tetras and Otto are fine), but can still go to a slightly yellow drop checker without any complaint from them.

finely tune delivery of the Co2 to maintain a very specific level
The easy way is to use some transparent tape from the office supplies shop and with that reduce the surface area at the bottom of the spray bar. 1 cm tape on a 90 cm spray bar yields a 1% reduction in CO2 absorption. I have also partially filled my circular tube, same thing as you suggest with the triangular shape, but then we need again a precision CO2 regulator :(

Just thoughts really but I feel maintaining the ability to easily adjust the Co2 level would be a ‘must have’ for a lot of folks!
it is as simple as this
1653430932534.png
 

Yugang

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Continued testing.

A drop checker mounted 10 cm from the bottom on the front (i.e. in the path of the spraybar) is going into the yellowish green, and for pH drop I consistently measure 1.5-1.6. Fish are ok, but I believe I should not go to even higher CO2 ppm.

If anything, I would change the spraybar to a slightly smaller size, and lower CO2, but for the rest it works very well. I am now using an old regulator, with a stability that I did not consider acceptable anymore for my reactor, but for the spray bar I don't bother about regulator precision.

With one or two more weeks of testing of the spray bar I may decide to disassemble the (not active since installing spray bar) reactor, and store it. Really not sure why I would ever use it again.


1653718301666.png
 
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Yugang

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A FTS by night. Huge windows and HK sunshine are a challenge making daytime pictures. Nightime with dimmed light and more relaxed fish is my favorite anyway.

1654434688641.png


Nice progress with testing my CO2 Spay Bar, but playing with CO2 always comes at a cost. I may need a few more weeks, some adjustments here and there, and hope to share my experience later on.
 

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Nick potts

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This is similar to what tropica and few others offer but with a better reservoir design and constant refill.

Tank looks good and good luck with the experiment.
 

Yugang

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similar to what tropica and few others offer
Would be nice to learn from what others have done, could you give a link please?

EDIT: Checking out Tropica website again and only find CO2 system with diffusor. This would be my least favourite (maintenance, stability, efficiency) method. Am I missing something @Nick potts , and could you help me please with links to similar solutions as you mention?
 
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Yugang

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Although my CO2 Spray Bar has been working fine since first installation in my tank, I continued with testing over the past few weeks with two objectives:
  1. I am probably not alone in being surprised that such a simple and powerful concept has not been developed before, and want to be sure there are no hidden problems or roadblocks. If ultimately it wouldn’t appear practically feasible, I would prefer to report that asap, forget the CO2 Spray Bar and go back to using my CO2 reactor.
  2. I hope that measurement data and detailed description can save time when implementing the concept in other tanks. We already have 3.6K CO2 threads, and have still not managed to demystify CO2. With a detailed description, CO2 Spray Bar can be simple and in my experience superior to diffusers and even reactors, with or without CO2 controller.

CO2 overflow

In the original design my Spray Bar would always be fully filled with CO2, with excess CO2 escaping at irregular intervals and with larger blurbs from the open bottom of the bar. I modified the design with a 5 mm hole (‘CO2 overflow’) as per below:

1654924672298.png


The water/CO2 meniscus is visible in the CO2 overflow, and small excess amounts of CO2 will escape at regular intervals (usually 30-120 seconds, depending on CO2 regulator setting). With this overflow I can optimise the CO2 regulator setting so as to minimize unnecessary CO2 losses, as well as the setting the dimensions of the CO2 reservoir by turning the white piece clockwise (less CO2 reservoir) or counter clockwise (more). With my current setting of the CO2 overflow I get a 1.4 pH drop, so I won’t change it anymore and pH drop will be stable over time within a few hundedths.

Note: if the CO2 overflow is drilled too small, less than 5 mm, it will not work anymore as the surface tension on the water will not allow bubbles to form under the low working pressure. 5-6 mm, and in this position works well, but I would be happy with a smart idea how to create even smaller bubbles from the overflow to further minimize losses.

Setting up the spray bar and CO2 regulator.

During weekly tank maintenance I take the CO2 Spray Bar out, as it is a bit fragile and I want to save myself an hour work and 4 GBP producing a new one.

Placement back in the tank takes less than a minute, using the trick to align the top of the Spray Bar exactly with the water surface.

As per the first posting in this thread, setting of the CO2 regulator is no longer precision work. Everything is fine and pH is perfectly reproducible as long as the Spray Bar remains full and there is some excess from the overflow. Just inject enough and watch the overflow releasing CO2 at some intervals, then dial down regulator only to save on CO2 consumption. I usually set CO2 regulator anywhere between 5 and 6 bps and don’t worry about further finetuning.

Testing stability / reproducibility

The benefit of the spray bar is that we do no longer need a precision CO2 regulator. I usually inject 5 or 6 bps into the spray bar. With 5 bps the spray bar fills slowly in the morning, and releases just one bubble per 60-90 seconds from the overflow after stabilisation. When I increase injection to 6 bps the Spray Bar will start releasing CO2 less than 1 hr after start up, and later on release CO2 from the overflow every 15-30 sec.

pH profile compared on day 1 with 5 bps, and day 2 with 6 bps. Degassed pH = 7.4, so both stabilize at 6.0 which is a 1.4 pH drop.
In all graphs I use raw data, no corrections. For some reason the starting pH on one morning is 6.52, other morning 6.73.
For a fair comparison of both curves we could measure the time from 6.5 down to 6.1, which is 3 hrs for both days. pH stabilises at 6.0 and remains within plus or minus 0.01 during the day, irrespective of CO2 regulator setting.

1654924856112.png


Full day pH curve

As the lowest pH is 6.0 with my current spray bar and setting of CO2 overflow, it is preferred to keep pH within 6.1 and 6.0 during the photo period. As discussed above generally 3 hours CO2 before lights on will be sufficient to reach 6.1. In the below graph I turned CO2 off at 14:00, and this allows 2 more hours during the photoperiod until the pH crosses the 6.1 level. After CO2 injection off, the Spray Bar gradually empties within typically 30 min.

(Note: have no explanation for the pH 0.02 irregularity at 15:15 )

1654924906658.png


In summary, I turn CO2 on 3 hours before photo period, off 2 hours before end of photo period.

Need for air release?

Most CO2 reactors have a valve to release air. This air may otherwise accumulate, creating noise and reduce efficiency.

I have not noticed significant issues with air build up in my spray bar, other than when I introduced bubbles topping up tank water from a bucket.

There are two easy ways to get air out from the spray bar. Turn it 90 degrees and back, or use a turkey blaster to suck it out. Both are quick and efficient, but the question remains if it is necessary at all.

When there is air trapped in the CO2 Spray Bar, the CO2 partial pressure will be lowered and efficiency of absorption in water is lowered as a result. However, with lower CO2 uptake by water, the reservoir volume grows quicker and the CO2 overflow releases bubbles faster. With each bubble that escapes the reservoir from the overflow, some air is purged out as well. Effectively, the more unwanted air is still present, the faster the CO2 Spray Bar gets rid of it.

I decided to test the theory with an extreme experiment – I filled the Spray Bar with 100% air in the early morning, just to see what happens. The result is remarkable, even with the extreme 100% air filling the pH curve is within a few hundredths of what it would be without any air. Actually the physics behind is more complicated than the graph suggests, I did some literature search as well, but will not elaborate on that in this posting. They key result is that the CO2 Spray Bar deals with trapped air through its operating principle, and the user does not need to worry about at all.

1654925010274.png
 

Nick potts

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EDIT: Checking out Tropica website again and only find CO2 system with diffusor. This would be my least favourite (maintenance, stability, efficiency) method. Am I missing something @Nick potts , and could you help me please with links to similar solutions as you mention?
 

Yugang

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Not longer offered by Tropica brand. Will not be a reliable CO2 solution for most tanks, and does not bring same benefits as CO2 Spray Bar.
 
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Nick potts

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Not longer offered by Tropica brand. Will not be a reliable CO2 solution for most tanks, and does not bring same benefits as CO2 Spray Bar.

Can still be bought and other companies offer the same.

While I agree not the same as your bar, it operates on exactly the same principle, passive diffusion of CO2 into the water column.

I also don't think the bar will offer a reliable and simple solution to most tanks compared to even budget reg and needle valve.
 

Gorillastomp

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Your system is interesting. I think this could be inserted in a sump without reducing the flow that the reactor brings in.
Probably less effective than a reactor for dropping the PH quicker.
 

Yugang

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I hope it is helpful to give a summary.

I tested various CO2 regulators, in-tank and in-line diffusers over the years, and most recent years worked with a reactor that I modified. For the CO2 Spray Bar I invested quite some time, and posted the measurement results in this thread for the benefit of other hobbyists.

From my experience (partially subjective, mostly based on facts and experience) I now believe that CO2 Spray Bar outperforms diffusers and reactor on almost all parameters.

1654996401182.png


I have decided to disassemble the reactor I have been using for years, which always worked very well. I am using my pH/CO2 controller now only for measuring CO2 profiles, but frankly see no benefits anymore using it to control my CO2 injection again.

The performance and benefits of my Spray Bar are too obvious and convincing for me, and I doubt if I will ever use my reactor (or pH controller) again.

If for some reason I get less happy with my CO2 Spray Bar, I will share with an update on this thread.

Thank you for reading!

P.S. I hinted in other threads that I have ideas for a new CO2 concept, that will outperform traditional regulators and even CO2 dream machine.
With CO2 Spray Bar however, I am not sure anymore if longer term there is a need in the hobby for more advanced technological concepts, regulators, diffusers or reactors.
I will let the CO2 Spray Bar ideas sink in, hopefully some others build one and share their experience, and later on decide if and how I share my other ideas.


1655000927845.png


CO2 Spray Bar nearly invisible...

1655023312693.png
 

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Yugang

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Do you find the CO2 concentration is dependent on how much flow there is over the bar? If you slow down the flow, does that decrease the amount of CO2 in the water?
I have not been able to test that, but I suspect that any reasonable flow will do. When I take spray bar out, mount is again, or change direction of water spray bar I find very little to no variation on pH profile.

From a physics perspective - stagnant water will create a boundary layer that will slow down absorption. But I would expect that any reasonanble flow will eliminate that effect and soon create a stable situation where only the surface area counts.

As said, day to day I find pH reproducible within 0.01 or 0.02, even after some adustments in the tank.
 

Andy Pierce

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Since the CO2 is dissolved in the water (rather than suspended temporarily as bubbles) I suppose it wouldn't matter where the CO2 bar was with respect to the water spray bar... you could probably but them both together at the back of the tank for a cleaner look. If the rate of the flow doesn't matter, it could be straightforward to calculate how much CO2 surface area you needed for a tank of any specified water volume.
You show the pH drop during the day, but how do you turn the CO2 spray bar off? Do you stop the water flow at night, or does the CO2 empty itself after you stop bubbling CO2 into the spray bar?
 

Yugang

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you could probably but them both together at the back of the tank for a cleaner look
I thought about mounting it on the back, valuable point. However at the front it is hardly visible, and I like the efficiency of dissolved CO2 going straight down to the plants, rather than having to travel the surface from back to front first.

it could be straightforward to calculate how much CO2 surface area you needed for a tank of any specified water volume.
The required surface area of the CO2 spray bar should be proportional to the surface area of the tank, not the volume. This is because outgassing of CO2 from tank surface is the main factor to determine the equilibrium CO2 ppm. Hope this is clear, I am happy to elaborate further. The volume of tank then comes into play in the speed of the ramp up in the morning.

You show the pH drop during the day, but how do you turn the CO2 spray bar off? Do you stop the water flow at night, or does the CO2 empty itself after you stop bubbling CO2 into the spray bar?
I stop the CO2 bar by turning solenoid off, 2 hours before I start dimming light.
Filter continues at night, spraybar is mostly empty some time after solenoid off.
 

LMuhlen

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I'm following your experiment and am itching to try it. But I feel that you didn't list in your table 2 important restrictions of the system, which are maybe prohibitive for me.

First it is closely tied to the filtration return being back to front. I can't do that in my setup, so the reactor gets a point here, it doesn't care how the water returns, there just needs to be circulation. I could use a spray bar, but it would need to be from side to side and the flow would probably lose its coherence when it reached the other side.

Second, it seems like it would suffer from evaporation and with the water level reducing. Again, the reactor doesn't care. So another point for the reactor.

I would add a line in your table with something like setup flexibility, where it loses to the alternatives. Still, I think it has many positive characteristics and I'm trying to find a creative solution to implement it here somehow.
 

Yugang

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First it is closely tied to the filtration return being back to front. I can't do that in my setup, so the reactor gets a point here, it doesn't care how the water returns, there just needs to be circulation. I could use a spray bar, but it would need to be from side to side and the flow would probably lose its coherence when it reached the other side.
This is correct. I believe that generally one needs a filter return spraybar over the full length of the tank, and the CO2 Spray Bar over full tank length as well.
For the CO2 Spray Bar to have suffcient capacity I believe the design rule in the OP is still roughly correct:
Design rules / estimation
For my tank (100 * 45 * 60 cm) I use a 1 inch, 90 cm long CO2 spray bar This is 216 cm2 surface area. The ratio between tank surface area (4500 cm2) and CO2 spray bar (216) is 20.8 :1. For other tank dimensions, this ratio is a good approximation how to find the optimal dimensions of the spray bar.
As @Andy Pierce noted, the CO2 Spray Bar could probably also be mounted on the back if that would be preferred.

While I understand that full length spray bars are not suitible for every tank, they have a big plus in terms of flow and distribution if they can be used. This was already known before I started thinking about the CO2 aspect. With a transparent tube they can be virtually invisible as you see from my FTs.

Second, it seems like it would suffer from evaporation and with the water level reducing. Again, the reactor doesn't care
This is actually my focus in the past several week's experiments. The point is, a reactor DOES care as do all setups that do not use a pH controller for stabilisation
In a traditional setup (no pH controller) CO2 is a balance created between injection, outgassing and consumption in the tank. This is irrespective of injection method (reactor, diffuser, spray bar).

The tank's outgassing is very sensitive to variations of surface agitation and flow, but no more for a CO2 Spray Bar than for a reactor or diffuser. I also learn that actually the morning's starting pH (as a result of outgassing but also plant and fish CO2 production during the night) can be quite variable

The CO2 Spray Bar does not care too much about water level, as long as it remains below water.

What I am currently monitoring is how I get the smallest (few 0.01 pH) day-to-day variations in CO2 ppm. I suspect that nearly nobody in the hobby manages this well. From my experience this challenge is no different with a CO2 Spray Bar than diffuser or reactor, it is inherent in the CO2 balancing act in the tank, when not using an active controller.

Until now I am using my pH/CO2 controller only as a pH monitoring device, but not to control the solenoid. If I actually start to control the CO2 system with Spray Bar the CO2 stabilisation problem is solved by the controller, while the CO2 Spray Bar provides the inherent safety for cases where the controller would fail and try to inject too much CO2.
I would add a line in your table with something like setup flexibility, where it loses to the alternatives.
I had a perfectly working reactor in my tank, but decided to disassemble and not longer using it. From my experience, and this is for my tank, the spray bar is better and I see no flaws that I wouln't have with reactor of diffuser.
My only doubt today is whether I would prefer a system with pH/CO2 controller (so easy to stabilise, but some points of potential failure), or just the CO2 spray bar with a simple CO2 regulator (needs a bit more experience to get CO2 stability over days and weeks).
 
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