CO2 Spray Bar - a summary

[Yugang]

Several members of this forum have greatly contributed to testing the concept of Horizontal CO2 Reactor , and I am so happy that collectively we have succeeded to push some true innovation. @Unexpected successfully pioneered the first horizontal reactor on his bigger tank, was kind enough to call it ‘Yugang reactor’ and inspired several followers with that. Also to mention @RickyV who took CO2 injection to a new level with a 1000-gallon system, achieving a 1.0 pH drop in just 38 minutes. Thank you to all who have contributed, and I believe hobbyist will find most answers in the Horizontal CO2 Reactor thread on this forum and hopefully feel that CO2 is easier than it used to be with bubble reactors.

My journey started about 2 years ago, when I was doing some measurements and calculations on my bubble reactor and got to the idea of the CO2 Spray Bar. I built probably 10 versions / prototypes of CO2 Spray Bar, spent many days measuring pH profiles, so that I could share my insights with the community on UKAPS. The horizontal reactor is based on the physics principles of the CO2 Spray Bar, and test results are applicable to both. I was at the time so happy with my CO2 Spray Bar that I gave no priority to building the horizontal reactor and thanks again to @Unexpected for his initiative and courage. I am currently also using the horizontal reactor, but my love and in certain situations preference for CO2 Spray Bar remains.

I discovered this morning that both threads on CO2 Spray Bar and Horizontal CO2 reactor have now been removed by the UKAPS admins. This may have happened in the past few weeks, not sure as I am not a regular UKAPS visitor anymore. These threads represent probably several hundred hours work, aiming to be a lasting and valuable contribution to the hobby, lots of measurement data, comparisons and calculations, and many pages of posts from fellow hobbyists. Even posts in several journals featuring the CO2 Spray Bar or Horizontal Reactor have been deleted or edited by admins. Thumbs up to forum rules, but very few will disagree that these all stand or fall with forum governance and integrity to individual members as well as the community.

While having the Horizontal CO2 Reactor now well documented on this forum, I believe it is a loss for the hobby if we would lose the insights on CO2 Spray Bar. It offers the same performance as the Horizontal CO2 Reactor, can be made for perhaps 5-10 USD and one hour DIY work. When I have more time I may create a new thread on this forum, with similar detail as what was deleted in UKAPS, with various prototypes and measurements. For now I hope it is useful if I just post a quick summary.

The first prototype CO2 Spray Bar, as I was testing late 2021 / early 2022.









The CO2 Spray Bar in the front of the tank, was in my tank barely visible. In my 200 liter tank I used a transparent half pipe, and achieved 1.5 pH drop with very good stability. It is from the experiments with the Spray Bar that I took the 17.7 ratio for the calculation of Horizontal Reactor dimension.

Some forum members pushed back on the idea having anything in the front, so I started experimenting with CO2 Spray Bar in the back of the tank.





I hope the above pictures help to understand the CO2 Spray Bar, and perhaps inspire fellow hobbyists to try it in their tanks. Having a simple half-pipe in a tank is easier than building an inline horizontal CO2 reactor, and may be especially attractive for small tanks.

For any further questions or help, please post below or send me an PM. I may start a more detailed thread when I have a bit more time and/or see there is interest from fellow hobbyists.

Thank you for reading, and thank you to ScapeCrunch for giving us a good home for our hobby.

 

[Unexpected]

If I had a standard tank, I’d definitely try this route. There’s something about being able to see the reactor in action. Having a simple adjustment option for overflow mode is really nice as well.

 

[Yugang]

Having a simple adjustment option for overflow mode is really nice as well.

Indeed, I used an end piece with off-centre drilled hole that I could rotate to dial in the position of the CO2 meniscus. Later, I discovered it is easier to have probably 5 different end pieces, each for one particular setting of the meniscus and thus one particular CO2 injection rate in overflow mode. No need to worry about precision CO2 regulator stability, as it is now the end piece and its definition of the meniscus that sets and keeps the CO2 injection rate stable.

IMO a better approach to having a good and stable (within the day, and from day to day) pH profile than the traditional precision CO2 regulator + diffuser, but commercially less attractive as it requires no more than a bunch of plastic parts and some DIY.

 

[Count Krunk]

I dont really get how it works yet. Would love to set this up in a 20g. How do you do the construction?

 

[Yugang]

I dont really get how it works yet. Would love to set this up in a 20g. How do you do the construction?

In its simplest form you just use one 'half pipe', that I constructed as follows:



On one side you want to drill the white end-piece with a 5 mm hole, that serves to define the CO2 meniscus and thus the reactor injection power

Drawing straight lines over the full length. I use an aluminium 90 deg profile to hold the tube, and permanent marker:



Then carefully cut with a hand saw. The blade is held nearly parallel to the tube's surface:




Remember that the physics of CO2 absorption in water are exactly same for CO2 Spray Bar and Horizontal CO2 reactor. For calculating the correct CO2 Spray Bar dimensions, aiming for a 1.5-1.6 pH drop, we can use the same 17.7 factor as described in the thread Horizontal CO2 Reactor. Calculate tank surface area, divide by 17.7 and with that have the minimum surface area for the Spray Bar.

I hope this answers your question and is helpful.
@Count Krunk please reach out with PM, I am always happy to help out where I can.

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Rebuilding the content of the UKAPS thread, I add a few more insights for clarification.
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Some insights on CO2 stability, short term (within the day) as well as long term (day-to-day, week-to-week) using the CO2 Spray Bar in different modes of operation.

Three alternative approaches to using the CO2 Spray Bar:

1. ‘Overflow mode’. We inject slightly more (5%-10%) CO2 in the CO2 Spray Bar than the CO2 absorption into the water. The CO2 reservoir remains always full, and see a few excess CO2 bubbles escape from the CO2 overflow.
2. ‘Regulator mode’. We use the CO2 Spray Bar below its capacity, so that the CO2 meniscus never reaches the overflow and no CO2 bubbles escape from the overflow. It is now the setting of the CO2 regulator that drives how much CO2 is absorbed in the tank.
3. ‘CO2/pH controller mode’. As Regulator Mode, no bubbles escaping from overflow, but rather than the regulator it is the CO2/pH controller that drives the CO2 injection rate.

Some general remarks on CO2 stability in tank (no CO2/pH controller)

• CO2 ppm stabilises when CO2 injection = CO2 surface outgassing + plant CO2 uptake. For a good CO2 stabilisation in the tank it is essential that CO2 outgassing and CO2 injection are both high enough. This follows from simple math, mentioned in several other posts, and will not elaborate again here. Irrespective of the injection method (diffuser, reactor, CO2 Spray Bar), a good CO2 stability can only be achieved with good surface agitation (gas exchange), and avoiding any changes in the surface agitation. Changes of the flow pattern and surface agitation (e.g. adjust spray bar or lily pipe) have a significant impact on the tank CO2 ppm and stability.
• For tanks with good surface agitation, a requirement for good stability, both injection and outgassing will usually be much higher than the plant CO2 uptake. Changes in plant mass, growth or pruning, do change plant CO2 uptake, but this is likely to be minor as compared to total CO2 injection and outgassing. With tank maintenance and heavy pruning, the change in waterflow may outweigh the impact of removing plant mass. Unless pH is precisely monitored with a probe, adjusting CO2 injection for plant mass may very well be counterproductive for CO2 stability.

1. ‘Overflow Mode’

As the meniscus of CO2 will align itself with the overflow, the CO2-water absorption area will be constant. With the CO2 Spray Bar mounted in front, and in the flow of the water spray bar the flow at the absorption interface is stabilised as well unless the filter clogs up.

The quality and stability of the CO2 regulator is no longer important, as long as it injects enough. In the thread of Horizontal Reactor
I posted an #156 analysis how much 'enough' really is, and how stability is affected by the CO2 excess flow. I usually set it so that I see a couple of CO2 bubbles escape from the overflow every minute, and then don’t worry any more. Monitoring flow rate and using a bubble counter is no longer needed, just watch the overflow in action and if it ‘runs dry’ increase the injection a bit.

I use different overflow end pieces, with the hole drilled in different positions to adjust the CO2 reservoir capacity to my liking. This works better than the rotation that I used to do, as it is important to rule out unwanted changes in the position of the overflow.

For levelling the CO2 Spray Bar horizontally, so that geometry is reproducible, I use the tank water surface as a reference, or alternatively a few bubbles of air or CO2 in the nearly empty spray bar.

The main factor that will drive both short term and long term CO2 stability are the surface agitation / gas exchange.


2. ‘Regulator Mode’

We set the overflow so that under normal operation the CO2 meniscus will never reach it, and no CO2 will escape from the overflow. The system will then stabilise when CO2 absorption = CO2 injection from the regulator, and we have a very similar function as with a traditional inline reactor.

Now, of course, we need a good quality CO2 regulator that is both short term stable, and has no long term (day-to-day and week-to-week) drift. we need to use a bubble counter to regularly monitor & finetune the injection rate

While the CO2 Spray Bar functions mostly as in inline reactor, it eliminates most of the traditional reactor’s challenges. No noise. No flow reduction for filter. No safety concern when a cylinder blow out or regulator malfunction causes too much CO2 injection. No CO2 mist in tank.

The main factor that will drive both short term and long term CO2 stability are surface agitation / gas exchange, as well as instabilities and drift from the CO2 regulator.


3. ‘CO2/pH controller mode’

As with Regulator Mode, but instead using a CO2/pH controller to stabilise pH within a given bandwidth.

While the CO2 Spray Bar functions similar to an inline reactor, as per above, it eliminates most of the traditional reactor’s challenges. No noise. No flow reduction for filter. No CO2 mist in tank.

With a proper setting of the overflow, it can be used to fully maintain the function of a correctly working pH controller, while mitigating risks sometimes associated with the CO2/pH controller. When the controller injects more than a safe level of CO2 (malfunction, probe or KH change) the CO2 overflow will act as a safety valve and limit the maximum CO2 that the Spray Bar can inject.

The main factors that will drive CO2 stability are the KH stability, calibration of pH probe, and upper/lower limits pH setting.

 

[Yugang]

I tested various CO2 regulators, in-tank and in-line diffusers over the years, worked with a AquaMedic reactor that I modified, then moved on to developing CO2 Spray Bar.

I am not really a fan of diffusers, they look fancy but no manufacturer thinks or talks about the actual result that matters - CO2 stability (within the day, day to day, week to week) and pH profile. Same applies to most CO2 regulators in the non-professional segment, I have not found any that enjoys really good customer feedback and performs stably over time and without at some point breaking down. This is one reason that I was looking for alternatives.

I posted the below on UKAPS, perhaps 18 months ago and before I got to the insights of Horizontal CO2 reactor. So the reactor mentioned here is a bubble reactor, that I optimised and was actually really happy with. From my experience (20% subjective, 80% based on facts and experience) I believe that CO2 Spray Bar outperforms diffusers and bubble reactors on almost all parameters.

Obviously this is open for debate, but I hope an interesting perspective both for hobbyists and manufacturers.



In summary and easier to read when not logged in:

• Unlike diffusers, we have (close to) 100% CO2 absorption efficiency. Note that CO2 mist or bubbles from diffusers, escaping to the surface, make it very hard to know how much of the injected CO2 actually dissolves in water, or indeed to guarantee that CO2 ppm is constant over time.
• Unlike diffusers, no maintenance required and the operation on day 1 is same as on any day in the future.
• Unlike bubble reactors, it is very easy to perfectly calculate and set up a CO2 Spray Bar for any size of tank, be it a nano tank or a swimming pool sized tank and achieve a 1.5 pH drop.
• Unlike bubble reactors, no noise, no mist, no bubbles escaping and zero loss of filter pump flow.
• 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 5-10% 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 accidentally 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 and fish keep doing their thing.
• 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.

 

[Art]

@Yugang I commend you for thinking about these things and working to push planted aquarium equipment innovation forward.

I don't want to make light of your design but is this not simply a revised design for a CO2 bell? The old design that I'm familiar with was filling a bell or other upside down container with CO2 while in the aquarium. The idea is that the CO2 would diffuse into the water following the principles of high and low concentration movement.

In your design, the upside down half tube is the bell that holds the CO2. Having the spray bar close and beneath it causes water flow to maybe quicken the diffusion into the water column and spread it around the aquarium in a much better fashion than the old bell design would.

Please don't take my comments as in any way negative. I just want to see if my understanding is correct.

 

[Yugang]

@Yugang I commend you for thinking about these things and working to push planted aquarium equipment innovation forward.

I don't want to make light of your design but is this not simply a revised design for a CO2 bell? The old design that I'm familiar with was filling a bell or other upside down container with CO2 while in the aquarium. The idea is that the CO2 would diffuse into the water following the principles of high and low concentration movement.

In your design, the upside down half tube is the bell that holds the CO2. Having the spray bar close and beneath it causes water flow to maybe quicken the diffusion into the water column and spread it around the aquarium in a much better fashion than the old bell design would.

Please don't take my comments as in any way negative. I just want to see if my understanding is correct.

Any water / CO2 gas interface will work to absorb CO2 in water. The challenge for the hobby is to control how fast CO2 absorption goes, to keep it stable over time, to have a continuous supply until we want to turn it off.

The CO2 bell was one of the earliest solutions to CO2 injection, a very logical one. Unfortunately, the CO2 bell design was not used for improved designs, but a few decades ago bubbles from diffusers and in bubble reactors became the norm. This provided more capacity in larger tanks, stability over time, and continuous operation for a full day.

I would agree that the CO2 Spray Bar is a modified design of a CO2 bell, but have yet to see a CO2 bell that gives a 50 gallon tank a consistent stability of only a few hundredths pH during a 10 hours light on period.

 

[anewbie]

I'm curious - can't you just take a 1.5 inch (diameter) of tubing and run it the length of the tank under the stand and have the water going to the return go through this tubing (for a 550 that would be approx 8 feet long) and would that not do more or less the same thing as a reactor but with greater diffusion surface? Perhaps I am missing something basic. Btw i decided to not turn on co2 for my planted tank for now as i'm getting results like this without co2:




Now i fully admit these plants are crypts which should grow fine without co2; i do have some ha'ra rotala as well as blood red and i fully admit it is growing but in a struggling form and lacks the strong red it had with co2 but adding co2 create new problems. Some plant over grow and as a large aquarium (this one is only 200 gallons); some plants grow too fast; and with such a large aquarium fertilization is a problem (i'm currently using root tabs around specific plants).

I do have co2 on my 550 but am on the verge of turning it off very slowly (reducing the amount of co2 i'm injecting till it goes to near 0); the problem is some plants simply get too large and with co2 you have to keep up with fertlizer or new problems happen that don't occur in a low tech tank growing at a slower pace. The 550 is 24 inch tall and 4 feet wide which makes plant management quite annoying esp in the middle region that is hard to reach.

 

[Yugang]

I'm curious - can't you just take a 1.5 inch (diameter) of tubing and run it the length of the tank under the stand

You may want to have a look at Horizontal Reactor

Indeed, exactly same process of CO2 absorption, same benefits, but as an inline version rather than in-tank solution as CO2 Spray Bar is.

 

[Yugang]

It's time to experiment with CO2 Spray Bar again. I am interested to explore what compromises I'll have to accept if when I inject much less CO2 than most high tech tanks. For the past weeks I have already started to reduce injection in my reactor, also reduced reactor size, but why not totally commit and use a small CO2 Spray Bar instead.

I have no idea what would be the minimum acceptable size, so I will try 5000 mm2 in overflow mode. For my tank, using the 17.7 ratio targeting a 1.5 pH drop, I would need 25000 mm2, so with this CO2 Spray Bar I go for 80% reduction compared to more main stream high tech. Conventional wisdom says I may regret, but let's see.

Reactor out, back to a small CO2 Spray Bar...



Here is the CO2 Spray Bar in the tank. The position on the side is not perfect, but let's see if it works. I am currently also using a lid on top of my tank, this is another experiment I am running to explore how far I can reduce evaporation when I need to hibernate the tank while a month or two travelling.



My pH probe broke down, and as I am very confident using the reactor in overflow mode I never decided to buy a new one again. This is how I plan to continue at least for now, use the plants as indicator of tank health rather than (time consuming) pH profiles.

 

[SingAlongWithTsing]

300 cm x 70 cm x 70 cm tank using the same idea. Not sure how much theyre injecting though

 

[Yugang]

300 cm x 70 cm x 70 cm tank using the same idea. Not sure how much theyre injecting though

They inject CO2 bubbles in the water stream, in this case the water spray bar, which is of course quite common with inline diffusers or injecting just before the filter intake. Even with a precision regulator it will be hard for them to stabilise CO2, as we see the bubbles blowing out and one never knows which bubbles will be absorbed in water and which will leave the tank undissolved via the surface.



As described earlier in this thread, the CO2 Spray Bar is a separate pocket of gas, in a tube separate from the pump water flow, where it is not bubbles that give the injection but rather the interface between gas pocket of constant size and a water surface.
Unlike diffusers, the CO2 Spray Bar dimensions can be calculated and injection power is then known and constant, no dependence on regulator stability, inherently safe, and no maintenance needed. I believe a small CO2 Spray Bar is in most aspects superior to a diffuser and especially useful for smaller tanks, but it will take time to be generally accepted as such.

 

[Yugang]

Buildling a CO2 Spray Bar is very easy, perhaps 15-30 min work, and cheap. In this post I share some details about optimising the CO2 Spray Bar for overflow mode.

As a reminder, overflow mode uses the constant area between a pure CO2 gas pocket and a water surface. When all relevant parameters are constant, laws of physics will give us constant rate of injection from the gas pocket into the water and we do not longer rely on the stability of our CO2 regulator.

• We need the surface to be constant, hence using an overflow so that the tube will always be filled to the same volume, irrespective of CO2 added or CO2 leaving the tube.
• We need the gas to be pure, not mixed with other gases that will alter the absorption efficiency for CO2.

A pocket of gas above a volume or aquarium water will give diffusion of gases across the interface so that partial pressures will aim for equilibrium. Pure CO2 in the gas pocket will try to raise CO2 partial pressure in the water (hence the injection that we aim for), but some other dissolved gasses (oxygen, nitrogen) in the water will want to diffuse into the CO2 pocket as they are also aiming for equilibrium. As I described in the reactor thread, we use the overflow mechanism to always keep the CO2 pocket clean and with that rate of CO2 injection constant without the need for manual purging:

Post in thread 'Horizontal CO2 Reactor - Yugang 鱼缸 Reactor'

Oct 8, 2023

Context

As described earlier, we could operate the reactor in three different ways

• 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...

• Yugang

• 
• 

So how is this relevant for CO2 Spray Bar?





When the tube is full of CO2 (and perhaps small percentage of other gases) we want to see from time to time a bubble escape from the overflow. This overflow bubble will be almost pure CO2, but will also take with it some of the traces of other gases and therefore keep the gas pocket in the tube nearly perfectly clean. I cut the tube, so that the bubbles will overflow from the left, as far as possible from the right where new CO2 gets injected and mixes with the gas pocket.

Note: I want to inject bubbles in the water, not straight into the gas pocket, so that I can count the bubbles. This is not strictly necessary, but nice to have.

What I now have is my third build, because my first was not exactly how I wanted it to work.
I started out without a simple half tube, and without having the overflow cut out on the left. The gas pocket meniscus would then perfectly align with the edges of the tube, but then unfortunately some of the injected bubbles on the right would not mix with the gas pocket but escape straight to the tanks surface. We don't want to see this happening, because we want the gas bubbles escaping to be not-perfectly-pure CO2 bubbles from the gas pocket, and do the cleaning job, rather than the perfectly clean CO2 from the injection.

With the current design, all injected bubbles on the right will mix with the gas in the tube, and all overflow is from the cut out on the left. The reactor will keep the CO2 close to perfectly clean, and no manual purging will ever be needed for a stable overflow mode.

I hope these small details help.

 

[Yugang]

I am experimenting with low CO2, and decided to push it down further with an even smaller CO2 Spray Bar. My new prototype is down in the middle in the picture, with as reference my reactor, the tube for the CO2 Spray Bar I have been using until now (15 ppm CO2 in my 50 gallon tank) and a diffuser.

The new CO2 Spray Bar has about 3.500 mm2, compared to the 25.000 of my reactor this now about 15%. I am using it in overflow mode.

 

[Unexpected]

I am experimenting with low CO2, and decided to push it down further with an even smaller CO2 Spray Bar. My new prototype is down in the middle in the picture, with as reference my reactor, the tube for the CO2 Spray Bar I have been using until now (15 ppm CO2 in my 50 gallon tank) and a diffuser.

The new CO2 Spray Bar has about 3.500 mm2, compared to the 25.000 of my reactor this now about 15%. I am using it in overflow mode.


View attachment 5633

This is going to be interesting. Could you post before and after pictures? Would be cool to see how it effects the tank.

 

[Yugang]

This is going to be interesting. Could you post before and after pictures? Would be cool to see how it effects the tank.

Yes, will do that in the other thread where we discuss middle energy tanks.

Post in thread 'In search of middle-earth - a quest for a middle energy tank'

Jul 22, 2024

I installed a drop checker at 2 dKH, this is a good indicator for CO2 in the range of 15 ppm. Its colour suggests that the tank is around 10-15ppm.

I continue to use the lid covering the tank, for an open tank CO2 would have been even lower but this may be a good start.

Can't do science with one tank and no statistics, but the least I can do is post a FTS of my tank today as a reference. Over the past weeks I have been rescaping and experimenting with lower CO2 as well as limiting gas exchange, but if I could keep the tank comparable to this going forward I would consider that a good...

• Yugang

• 

Two weeks into the experiment I see my tank recovering quite well from lowering CO2 (30 ppm down to 15 ppm). Rather than giving it a second shock later I decided to push down right away and discover where is the limit. If I've gone too far, I can change back to my 15 ppm CO2 Spray Bar.

I am posting here specifically about CO2 Spray Bar, as I hope that gradually a few more users start to see the value. It is in my opinion far superior than an in tank diffuser, especially in overflow mode.

 

[Art]

@Yugang I know how you feel about user banners but, my friend, I really wish I would create one called "Inventor Extraordinaire" for your work with the reactor and innovating on CO2 delivery. I want to thank you for all of the thought you put into this and how you share it with the community.

I speak to everyone that joins and many have told me they have joined ScapeCrunch to follow your reactor threads. Well done, my friend.

 

[Unexpected]

Second that @Art

 

[Yugang]

@Yugang I know how you feel about user banners but, my friend, I really wish I would create one called "Inventor Extraordinaire" for your work with the reactor and innovating on CO2 delivery. I want to thank you for all of the thought you put into this and how you share it with the community.

I speak to everyone that joins and many have told me they have joined ScapeCrunch to follow your reactor threads. Well done, my friend.

Thank you for your kind words @Art, and for creating a platform for sharing ideas for the hobby.

My motivation is giving back to the hobby, helping fellow hobbyists as much as I can, and if possible to bring some sustainable progress with new ideas that stick for DIY and even in commercial products that can be widely available.

The reactor has been really busy for a year or so, but seems now to be well understood and needs less support. Besides, I am a big fan of using the CO2 Spray Bar for lower levels of CO2. Surprisingly, even though I posted earlier about the CO2 Spray Bar than the reactor, this has not gained much traction yet. We'll see, but my bet is that in a few years many hobbyists will have discovered how easy CO2 can be for small tanks with a CO2 Spray Bar in overflow mode, and then won't see a case for spending on precision regulators and diffusers, or even have to worry about CO2 injection rate and stability. CO2, I hope, will become one of the easiest parts of a successful tank.