# Other Aquarium Forums > Equipment and Accessories >  DIY CO2 reactor (Tom Barr's design)

## stormhawk

After some delays I finally decided to construct my own CO2 reactor based on Tom Barr's design that he posted on his own website.

I made a design flaw however, I did not use an angled joint to attach the reactor to the output head of the pump therefore there's always a bubble of air stuck at the top rear end of the reactor's body. Anyway, it seems the turbulence of the output flow is enough to break up the bubbles anyway. I'll do another version in the days to come.

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## Green Baron

> 


All,
Peter Gwee posted Tom's design here.

Jianyang,
Isn't the outlet supposed to face downwards so that the venturi can work as designed ?

Peter,
How does this design mixes the CO2 with water ? Won't the CO2 bubbles get flush out by the water current from the power head ?

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## stormhawk

On a sidenote, has anyone here made his/her own version of this reactor?

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## stormhawk

Gan, the thing is, there was supposed to be an angled joint to ensure that the flow of the powerhead goes in a circular spin in the reactor body. I missed that bit so this version is a little flawed. 

About the output tube for the CO2, I was trying to cut it shorter but ended up cracking part of it. So I just cut it anyway and now the bubble goes out from the side of the tube. Works anyway.

The bubbles are not fully dissolved since I forgot to use the angled joint but they are somewhat reduced in size once the flow of the powerhead gets to them.

I intend to modify this reactor soon when I get the angled joint or when I'm able to make some form of blockage in the reactor body to ensure that the flow goes in a zig-zag formation, thus ensuring that the CO2 has a longer time to dissolve.

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## ruyle

Jianyang,
That is certainly a pretty green you have there. It really blends with all
the other greens  :Laughing:  You want me to send you some viewtainers that
have black caps? They are 2" by 4" in length. Up to you....there's also
a side-mounted version of this reactor developed by a guy in Nebraska
that works very well. I could send you a copy of his plans, don't have
a scanner to use to paste up here, since it's hard copy.

Bill

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## stormhawk

Hi Bill,

Sure thing, I'll send you my address via email.  :Wink:

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## ruyle

> Hi Bill,
> 
> Sure thing, I'll send you my address via email.


Okey-dokey!  :Smile:  

Bill

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## Green Baron

> Gan, the thing is, there was supposed to be an angled joint to ensure that the flow of the powerhead goes in a circular spin in the reactor body. I missed that bit so this version is a little flawed.


Ok, now I get it. I missed that small angle joint. So the water is suppose to spin, just like that of internal CO2 reactor. 

For those who already have internal CO2 reactor, they can just connect the power head outlet to the inlet of the CO2 reactor and add a venturi to address the gas build-up.

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## PeterGwee

> For those who already have internal CO2 reactor, they can just connect the power head outlet to the inlet of the CO2 reactor and add a venturi to address the gas build-up.


Yep, just drill a small hole about 2" from the top of the tube for the venturi action and another 2.5" down opposite the venturi hole for burping. Just make sure to invert the powerhead such that the water intake hole is pointing upwards to enable burping once the power is off or else the powerhead will airlock once it starts again in the AM times. Main key with this reactor is to keep the bubble at the top portion of the reactor for as long as possible.

Regards
Peter Gwee

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## PeterGwee

Jianyang, the orientation of the outlet should always point down as pointed out by Gan. I made mine of those green taiwan bioball reactors. Simply extend the CO2 inlet via a rigid tubing to the inner hole of the CO2 inlet (the entire chamber becomes a bubble counter). The powerhead is side mounted and all you need is simply to drill 2 holes at the side of the reactor chamber (one for venturi and the other for burping.).

Regards
Peter Gwee

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## Green Baron

> The powerhead is side mounted and all you need is simply to drill 2 holes at the side of the reactor chamber (one for venturi and the other for burping.)


Peter,
Do you know why Tom has the CO2 outlet pipe extend so far down ? In those green bioball internal reactor, the CO2 outlet is at the top.
Also do you know what is the purpose of the venturi loop ? It sucks up the air (CO2+O2), funnels it into the power head and end up back into the reactor ?

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## PeterGwee

> Do you know why Tom has the CO2 outlet pipe extend so far down ? In those green bioball internal reactor, the CO2 outlet is at the top.


The whole idea is to use the reactor chamber to double up as a bubble counter.




> Also do you know what is the purpose of the venturi loop ? It sucks up the air (CO2+O2), funnels it into the power head and end up back into the reactor ?


For O2 degassing..Yes some CO2 will be wasted along with the O2 but that is not a big issue.

Here is a quote from Tom over APD which should explain things better since its directly from the horse's mouth...



> I've been secretly doing some test using a DO meter, chamber tubes and an IR to see about gas build up and efficieny of CO2 reactors. Perhaps not radical, but few have really looked at this issue in this much detail.
> 
> O2 levels are directly correlated and proprotional to gas bubble build in CO2 reactors, wereas the CO2 levels are not. 
> 
> In testing this idea, I needed to maintain the CO2 level. This was a problem since at higher levels with plants, the O2 levels exceeded saturation and outgassed in the chambers.
> 
> We have all seen this gas build up occur diurnally as the photoperoid progresses throughout the day. Many folks have asked why this occurs. Well, rather than sitting around wondering...........
> 
> This off gassing of O2 greatly reduces the efficiency of a CO2 reactor when you need it most, near the last half of the day.
> ...

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## FC

Sorry but when I see people starts adding equipment (if they can avoid) into a planted tank, I cannot help but to tell them "no".

In my opinion, a proper planted tank should maximise the splendid of the plants it contain and minimise any intrusions/intruders that might spoilt / disturb / discount its' magical touch. See below picture, you will know what I mean.

I am not saying my setup was anything fantastic but the absence of unecessary equipment helps alot. I have only 2 filter tubes in my tank at left back corner. I am using external CO2 reactor (DIY), the best and only type of reactor I would recommend. The far second that I would accept (in absence of external filter) is the pollen glass diffuser which has diminishing size.

The Tom Barr's reactor is efficient (methodlogy: re-circulation) but it is totally unsightly in the tank (like "Luohan" tank's look) and the addition of pump adds heat to the water. As for bubble counting, rely on nothing but a proper and dedicated bubble counter. Tom Barr, if you see this, excuse me for my blunt comments.

A good external reactor (buy or DIY) is the ultimate:
1) CO2 dissolve rate which easily exceed 90%
2) Can be placed anywhere in cabinet
3) Maintenance free for years
4) Stable performance
5) Just require existing external filter to drive
6) Almost faultless

CO2 injection when understood is nothing mysterious but a fairly simple process of getting CO2 dissolved in the water column. The off-the-shelve external reactor may cost a fair bit more ($70 onwards) but you get the ultimate and rid you from trying to engineer one. Of course, there are people like me who cannot keep their hand idle and decided DIY  :Very Happy:  .

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## stormhawk

Freddy, my tank is currently dismal at best, unless you count the massive growth of hornwort and duckweed, which I like alot.  :Laughing:  

I made this thing just for a tryout. I might however try and make a less unsightly version. If this reactor was placed behind a bed of tall and thick-growth Vallisneria, then it won't even appear in the image. I placed it up front so that I could take a look at it. Besides, it cost me less than $5 to DIY this thing.  :Wink:  

You're right about one thing, we don't need that many gadgets for a planted tank.

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## PeterGwee

Freddy, while the inline method with a canister filter is popular due to reduction in equipment in the tank, there are potential drawbacks. First is efficiency reduction once the filter flow slows down due to clogging. Once that happens, your CO2 is definitely going to drop. A small powerhead will drive the external better ime. Simple and does not clog readily like a filter does and even if it does, its simple to clean.

Regards
Peter Gwee

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## timebomb

> I am not saying my setup was anything fantastic


You don't have to be so modest, Freddy. Your tank is really "wow". The plants are growing so vibrantly I'm envious.

I'll be getting in touch with you one of these days when I'm ready to redo my big tank. 

Loh K L

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## FC

Jiang Yang,

There is nothing wrong, it is good do DIY, it helps in learning process.




> Freddy, while the inline method with a canister filter is popular due to reduction in equipment in the tank, there are potential drawbacks. First is efficiency reduction once the filter flow slows down due to clogging. Once that happens, your CO2 is definitely going to drop.


Not quite, you must have a bad reactor. A good reactor, will last you years without a single service, without clog, without slow down in flow. And provide you stable performance.
I will put up my DIY to share with you when I have time.

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## SnyperP

I believe Peter is trying to say that the output flow of the filter will slow down due to clogging and not the reacter itself. Although i do agree with you with the minimalistic view on equipment inside the tank, but sometimes it is not possible due to budget constraints. For myself, i cannot afford an external filter to drive such a unit so an internal reactor that cost $15-20 to build will have to do.

Peter, if you could take a moment and answer a question for me. It is concerning the venturi loop. I'm not quite sure what it's purpose is. I read the quote from Tom Barr, but I am still alittle confused about it. What i can say is i have noticed the gas bubble up inside the reactor during the later stages of my photoperiod and it is usually gone by morning. What i'm confused on is what the loop actually does. I've understand that the venturi pulls the water back into the system, but how does this increase the efficeny of the reactor while there is a high presence of O2 in the reactor?

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## SnyperP

Well i think i'm about to answer my own question. =p

Anyways, the venturi loops allows any gas built up at the top of the reactor to be pulled back into the system and broken down into a mist of bubbles. This will allow for better diffusion of the gasses into the water. Essentially, it removed the large gas bubble (if it forms) at the top of the reactor allowing the unit to perform properly. 

Sometimes i wish i would think about something for a few more minutes instead of asking questions. =D

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## FC

Phi Dang,

Yes, it is what I termed "re-circulation". You can find this in the cleverer and more elegant Dennerle reactor, only mechanically different.

Yes, the filter flow does slow down. It's time to wash filter which required maintenance/cleaning  :Laughing: . For any proper setup, one should consider the right filter (filter medium volume and flow rate) to cater for, other than the usual needs, the long lead time between services. For that, it should last at least 3 months and typically up to 6 months. These keep the owner peace of mind and concentrate/enjoy on plants and fishes, etc they keep. Depend on tank sizes, for large tanks, one good filter is the Eheim 2060 which has large tub that allows good consistence flow.

Planted, marine, animals, fish only, etc tanks should be beautiful and give a splendid feel whenever one look at it. So, one of the fundamental is to keep subject as pure as one can get. In another words, no unnecessary intrusions, the tank and the target subject only. That's what all professional tanks do to produce and impress that picture to hobbyists (see below pic). Therefore, this is an important tank foundation and fundamentals.

Having limited budget does not mean one should compromise the fundamentals of tank's beauty (one single most important happy factor for hobbyists). One can be patient and save a little for it. Good DIY is another cost savings. See below for my first S$15 modified reactor. Cheap and good.

See below for my present S$45 DIY reactor. More than enough for my tank.

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## imported_bpt

Freddy, it's a very beautiful aquarium. And definetely, minimalizing the equipment do make the difference. 

Right now, I'm using internal reactor like that green one in your external, with a 1500L/H internal pump, still there are pocket of CO2. Not to mention the uglier scene with this bulky thing.

I'm not good with DIY. I tried once to built an external reactor, but it leaked terribly and came loose after a while  :Opps: . I'm sure I used a wrong glue here. I used regular aquarium silicon glue to attach the plastic(transparent L shape) CO2 fitting to the PVC body. So, what glue do you use ?
Could you share how you build yours ? Seems that you have 2 reactors inline.

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## FC

Budi,

For the green reactor, get the extra long version. Do these:
1) Disassemble the reactor and remove those floating balls, they are useless.
2) Tape round the inner tubes tightly with teflon tape, about 2~3 rounds.
3) Apply some vesseline grease before you put the tubes/caps togther again. Make sure that the teflon tape seal the tubes evenly, re-do if necessary.

Now, you need to make these tubes/caps joined permanently by:
1) Clean/degrease the tube's external well.
2) Apply "super" glue (fast drying glue which is very effective for plastic) around the joins.

Now, you have a good and cost effective external reactor that is maintenance free.

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## Green Baron

> Budi,
> 
> For the green reactor, get the extra long version. Do these:
> 1) Disassemble the reactor and remove those floating balls, they are useless.
> 2) Tape round the inner tubes tightly with teflon tape, about 2~3 rounds.
> 3) Apply some vesseline grease before you put the tubes/caps togther again. Make sure that the teflon tape seal the tubes evenly, re-do if necessary.
> 
> Now, you need to make these tubes/caps joined permanently by:
> 1) Clean/degrease the tube's external well.
> ...


Budi, 
I used to use the same DIY green external rector and I joined them up permanently using super glue and reinforced by super stength tape on the outside. Unfortunately the joint came loose twice and flooded my living room  :Crying:  . The first time it happend a few hours before I am leave for US and the last time on my way back from Malaysia ! I think it must be the stress from the hoses over time which caused it to give way. 

Anyway I decided to switch back to internal reactor as I know should it happens again, I will have to remove all my fish tanks from the living room ! If you decide to DIY, I would suggest go for those water filter canister (the later version in Freddy's photo) instead of the green tube. !

BTW, I am now using a short internal green reactor with only 1 ball and driven by a Eheim 2026. The CO2 dissolve rate seems to be very good as there is no built-up of CO2/O2 in the reactor.

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## Green Baron

Freddy,
I like your 2nd DIY reactor. Where can I get such a canister ?

Do you have problem with dirt/mulm built-up in the reactor. I have this problem and whenver I stop and restart my filter, all the dirt get pushed back into a tank and the water becomes really dirty  :Sad:

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## FC

Yes, the 2nd DIY is more reliable. For the first DIY, you need to glue it after the aseembly and on the outside because the glue cannot handle water well.
The 2nd DIY is the common water filter canister that is available in hardware shop at about $35.
No, the mulm does not build up because I had anticipated this and built into my design. See picture. The reactor has been running since Aug 03 without a single cleaning.

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## amitava

Hi Freddy,

Can I have a basic diagram of your second external reactor?

regards

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## Green Baron

> No, the mulm does not build up because I had anticipated this and built into my design.


What did you incorporated in your design which prevents the mulm build-up ?

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## imported_bpt

Great information guys  :Idea:  
So the green reactor has some risk for external use. I kind of worry of that too, considering it is only pushed. But, I will give it a try per your instruction. Freddy, the canister reactor seems threaded, you didn't permanently glue this one right? And where is the inlet for CO2 in this reactor ?

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## stormhawk

> Originally Posted by fc
> 
> No, the mulm does not build up because I had anticipated this and built into my design.
> 
> 
> What did you incorporated in your design which prevents the mulm build-up ?


I think its the presence of the ceramic rings in the reactor.  :Wink:

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## FC

Good questions, I hope I can offer good answers.
Mulms
It is not possible to filter them because they are dissolved waste and bacterias which were built up over time. So, acknowledging that, I allow them to continuously flow back into the tank. They will be either attached to plants as benificial bacteria colony where the grazing SAE/Otto would take care of over-building, or settle in gravel.
It's a pity that I do not have the habbit of taking pictures of my DIY. Anyway, I acheive that by having a tube in the middle of the filter where it sucks any slightest mulm build-up at the base and return to the tank. The plastic tube with some side (drilled) holes is connected to the return port of the canister's cap. The tube is made short about 1 cm before it touches the canister's base.
CO2 Injection Point
To improve long term reliability and efficiency, I used a rare "T" tube made by Aqua-Medic and inject CO2 immediately after the filter's output (which is, of course, before the reactor).
Reliability Question on the Green Reactor
Frankly, before I found the right way (mentioned), I had experienced flooding my living room twice. To eliminate the risk totally, you can actually place the reactor before the filter, at the suction side. In this way, the reactor is under constant negative pressure which "vacuum" the reactor tight. However, you need filter flow rate of at least 1,000 L/Hr (like Eheim 2260 or larger) for this to work properly. With this flow rate, it would perform and has no issue on acidity on the filter's bacteria because the dilution is great enough.
One more point to note is that do not allow the tubes that are connected to the reactor to have twisting/bending force on the reactor. So, after the connection, adjust/position the tubes to allow the reactor to rest in peace. If possible tie the reactor to a wall (cabinet or filter) and away from usual your hands' traffic.

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## Green Baron

> Originally Posted by GanCW
> 
> 
> 
> 
> 
> 
>  Originally Posted by fc
> 
> ...


How does ceremic rings prevent mulm build-up ?

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## stormhawk

Beats me, but that's what I see in Freddy's picture. :P

I think he explained in his earlier post about allowing the flow-through of mulm. Since the ceramic rings do not block out the smaller particles, I think the mulm just basically flows through the gaps and holes amongst the ceramic rings and back into the tank.

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## Green Baron

> Beats me, but that's what I see in Freddy's picture. :P
> 
> I think he explained in his earlier post about allowing the flow-through of mulm. Since the ceramic rings do not block out the smaller particles, I think the mulm just basically flows through the gaps and holes amongst the ceramic rings and back into the tank.


I have ceremic rings in my external reactor as well but the mulm still get stuck in the reactor. Everytime I restart the pump, they all flow back into the tank :-(

Freddy,
Can you explain how you prevent mulm from accumulating in your reactor ?

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## FC

Hi Gan,

Sorry that I did not explain well enough. In the middle of the canister/reactor, there is a plastic tube (diameter 12mm filter eheim-style tube). The tube is connected to the output port of the canister (located at the cap's centre) and extended downwards and stop short of about 1cm before the canister's base. Therefore, any mulm accumulated will be constantly suck out and throw into the tank. You will not notice the mulm at all as it is discarded in small spacks. There is another reason for this design, to ensure maximum CO2 dissolve rate as the water/CO2 have to go a long way from top, through the ceramic rings and then down to the base before it is thrown to the tank.

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