# built up gas in DIY external reactor



## TexasRock (Feb 28, 2006)

How do I take care of this? 

Here's my specs on my reactor... 

24" long.
2" PVC pipe
I have a dedicated 350gph pump running it. 

Why do I end up with gas build up everyday? 

Keith


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## NE (Dec 10, 2004)

One reason could be if the reactor is connected on the suction side of the pump, then it's harder to dissolve the gas, the reactor should be connected on the pressure side for best performance.


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## ChrisC (May 15, 2006)

Are you running DIY Co2 or pressurised? DIY Co2 produces a very impure version of the gas. This could be a build up of impurities which won't dissolve as well.

Thanks,
Chris


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## TexasRock (Feb 28, 2006)

NE,

I have the reactor connected to the output of the Mag 3 pump...



Chris, I run pressurized CO2.


Thanks!

Keith


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## Chris S (Feb 27, 2006)

ChrisC said:


> Are you running DIY Co2 or pressurised? DIY Co2 produces a very impure version of the gas. This could be a build up of impurities which won't dissolve as well.


 What are the impurities that are developed with a DIY yeast reactor?
Could you please explain a bit further? I use DIY for the moment and i was unaware of this.


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## diablocanine (Jul 25, 2004)

TexasRock said:


> How do I take care of this?
> 
> Here's my specs on my reactor...
> 
> ...


Here is the pic you sent me, I'll post it for you.










I do not know why you are getting gas build up. Where is it building up? On my reactor, I have the CO2 entering further downstream. I also have bioballs inside the reactor and the reactor is the same diameter throughout. I thought you had built one like mine, here are the two I built. Maybe someone with your design can help...DC


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## KeIgO86 (Jun 23, 2005)

Gas build ups at the end of the day are very common. Most of the gas would be oxygen. 

I deduced this from a simple experiment:
* I ran a constant rate of pressurized CO2 into the reactor.(2bps)
* Lighting period was also constant throughout. (12hrs/day)
* For the first week, I pumped 5 wpg of lighting into the tank.
* I found a large colomn of gas build up in the reactor at the end of everyday day. (The tank was pearling like crazy)
* For the second week, I downgraded the lights to 3 wpg of lighting to the same tank.
* With the same rate of CO2 input, there was a minimal build up of gas in the reactor at the end of everyday. (The tank wasn't pearling as well as in the 5 wpg times)

Therefore, i deduced that the gas build up in the reactor is not undissolved CO2 but mostly oxygen as it would be hard to dissolve it in oxygen saturated waters at the end of the day. In fact, it would work the other way and dissolved oxygen is turned into gaseous state when water is interacting with CO2 gas in the reactor as the oxygen levels in dissolved and gaseous states are trying to achieve an equilibrium.

*I will not say for sure that I am definitely correct as I did not test the gas build up in the reactor for oxygen. But in the experiment, the only difference in the 2 setups were more light, which means more photosynthesis, which leads to more oxygen. Concentrations of other gases should remain largely unchanged. Thus, my conclusion.


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## TexasRock (Feb 28, 2006)

So do you have to burp the reactor everyday or let it be?

Keith


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## TexasRock (Feb 28, 2006)

Diablocanine,

I'm going to build one EXACTLY yours today after work... I have all the necessary parts already. As you can see from the pic... I bastardized my original one that was like yours and I tried to add an air line that I could bleed the build up out of... all of this to no success. I currently have the CO2 line running into my pump that operates the reactor. However, I'm going to scrap that one and build a new one later...

Keith


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## redstrat (Apr 3, 2006)

KeIgO86 said:


> Gas build ups at the end of the day are very common. Most of the gas would be oxygen.
> 
> I deduced this from a simple experiment:
> * I ran a constant rate of pressurized CO2 into the reactor.(2bps)
> ...


I'm going to have to argue that this is probably not true, can't really say for sure but I have read that CO2 does not actually displace dissolved O2 in water. I have read that CO2 will dissolve the same in water highly saturated with 02 just the same as O2 free water(I'll have to see if I can find that source again to verify). When your fish die because there is to much CO2 they aren't dying because there isn't enough dissolved O2 in the water its because the osmotic pressure of dissolved CO2 is to high around their gills and they can't get enough CO2 to respirate out of their bodies. Plus we are only injecting CO2 at a fraction of the concentration of dissolved O2.

well here is one place I've read it but I know there are others. 
http://www.hallman.org/plant/booth1.html
_"QUESTION: Isn't CO2 harmful to fish? 
In high concentrations, CO2 can block the respiration of CO2 from the fishes gills and cause oxygen starvation. Since the gills depend on a CO2 concentration differential between the levels in the blood and the water to transfer gases, high levels in the water will reduce the amount of CO2 that can be transferred. Although different references have wildly varying values for toxic levels, a concentration of below 30 ppm is definitely safe. Plants do best at around 15 ppm of dissolved CO2. 
It is a common misconception that water can hold only so much dissolved gas and adding CO2 will displace oxygen. This is not true. As a matter of fact, if enough CO2 and light is present to enable vigorous photosynthesis, oxygen levels can reach 120% of saturation.

Even at night, when the plants stop using CO2 and start using oxygen, the oxygen levels will stay about the same as a typical non-planted aquarium. "_

Most likely the excess gas in your reactor is undissolved CO2, reason being lack of contact time, not enough turbulence in the reactor, to large of bubbles, places the bubbles can get stuck and out of the flowing water, lack of enough flowrate. ect ect ect. 
in your experiment, did you have a PH controller on your system or was it just set at the same bubble rate for each trial. If you do have an automated system you would be pumping much more CO2 into the 5wpg setup because it woudl be consumed by the plants and the excess would be undissolved because of an inadequate reactor for that CO2 bubble rate. 
One of the biggest differences I've seen in DIY reactors vs. Commercial versions is the shear lack of size in the DIY reactors, most commercial reactors seem to have large difference in in/out pipe vs reactor diameter like 1/2" or 5/8" to 3" or so dia. and the 3" dia section is packed with bio balls.

*Granted, I'm taking all of this from things i've read about co2 injection and planning my own reactor for my setup that I dont really have yet so take it for what its worth. *

My current setup injects CO2 directly into the aquarium through the intake of a 300gph powerhead with Rena Micro filter floss over the output. you can see all the tiny bubbles dissolve/disappear immediately after coming out of the pump (pretty ridiculous to watch). Considering this, maybe you should find a way to break your bubbles into many smaller bubbles.


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## KeIgO86 (Jun 23, 2005)

Hi Texasrock,

For me, the gas build up usually totally dissolves during the "dark" period so when the next photoperiod starts, my reactor is totally clear of any gas. Just water and a spinning bioball in my internal reactor. Thus I don't see the need to burp my reactor at all since i doubt that the rate of solution of CO2 would be significantly reduced at all by the gas build up in the reactor (at least for that amount in MY reactor).

I'm not too sure if your in-line external reactor can dissolve all the gas before the next photo period. If it can, I don't see the need to burp. If it cannot, you should start burping or else you'll see a huge build up by the end of the month!

By observing how flowing water is interacting with the gas in the reactor, my guess is that the greater the concentration of the oxygen than CO2 in that gas colomn, the slower will be the rate of solution of CO2. (As there would be less chance of CO2 interacting with the water in this case, since much of the interaction will be with O2)

Hi davis.1841,

With regard to your question, I am using simply just a solenoid hooked up with the same timer as my light. No high tech gadgets like pH monitors etc. Its too expensive and I find no use for it, especially when i do not keep any sensitive fish/plants in my tank. I believe that will solve your question on whether I was pumping the same amount of CO2 into the reactor for both trials.



davis.1841 said:


> I'm going to have to argue that this is probably not true, can't really say for sure but I have read that CO2 does not actually displace dissolved O2 in water. I have read that CO2 will dissolve the same in water highly saturated with 02 just the same as O2 free water


I agree with you that the rate of solution of CO2 is largely if not totally independent of the amount of O2 in the water. Thus if we compare the 2 experiments, all parameters including rate of CO2 input and solution are identical, with the exception of lighting.

In that case, we "should" have equal gas build up in the reactor for both settings. But in the high light setting, we actually have a much greater gas build up. The difference in the volume of the colomn of gas build up in both settings at the end of the day is almost 300%. Where has this astonishing amount of gas build up come from? As stated earlier, the only different parameter is lighting, thus also the difference in rate of photosynthesis and oxygen concentration in the water.

Thus it would be rather contradictory of your above statement to say that gas in my reactor is undissolved CO2. At least that would be for the observations in my experiment.

Hope that will clear some of your doubts.


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## diablocanine (Jul 25, 2004)

1.5" PVC, 1.5" bio balls. Use a screw on end so you can add/remove bio balls as needed. Water in at the top, out at the bottom.....DC



TexasRock said:


> Diablocanine,
> 
> I'm going to build one EXACTLY yours today after work... I have all the necessary parts already. As you can see from the pic... I bastardized my original one that was like yours and I tried to add an air line that I could bleed the build up out of... all of this to no success. I currently have the CO2 line running into my pump that operates the reactor. However, I'm going to scrap that one and build a new one later...
> 
> Keith


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## TexasRock (Feb 28, 2006)

DC,

How long should I make it? It will have a dedicated Mag 3 pump running it. Would I be better off using 2" PVC or stick with the 1.5" like you suggested?

Keith


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## diablocanine (Jul 25, 2004)

I think I made it around 16". I used 1.5 because that is the size of the bio balls I have. I do not have any problems with the ones I made. I have made a few for other folks too and they report no problems. Do not know how it will work with a mag drive, shouldn't matter though....DC



TexasRock said:


> DC,
> 
> How long should I make it? It will have a dedicated Mag 3 pump running it. Would I be better off using 2" PVC or stick with the 1.5" like you suggested?
> 
> Keith


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## nopain00 (Jun 12, 2006)

*Solving trapped gas problem*

Though my DIY CO2 reactor design is different, I noticed the same problem of trapped gas at the top in my initial designs and was able to correct it by applying back pressure. I apologize in advance if the following explanation is lengthy, but I thought other members might be interested since related points were raised in the thread.

First, I determined the composition of the gas using a simple flame test, as is often used in an intro chemistry glass. I captured the trapped gas into a test tube (though any small container such as a pill bottle would do). Placing a lit match into the tube and observing the flame told me the identity of the gas.

Oxygen would cause a sudden pop as it combusted. Regular air would cause the match to extinguish only very slowly if the tube were deep enough as the oxygen was used up. Pure carbon dioxide (100%) would cause the flame to extinguish quite quickly since there would be no oxygen present.

As controls for the experiment, I tried the flame test in an empty (i.e. room air) tube and one filled with CO2 from my pressure tank. For fun, I also tried the O2 test using oxygen from a welding tank to fill a test tube. I performed all tests with the test tube right side up (mouth up). I found that in the experiment with trapped gas from the reactor, the flame extinguished more quickly than in room air, but not quite as quickly as the one filled with 100% carbon dioxide.

This makes sense since the most likely source of the gas is undissolved CO2 from the pressurized tank. This causes an air-water interface. Over time, an equilibrium is reached in the reactor between the gasses dissolved in the water and in the air (injected CO2 + room air). As CO2 is constantly added, the composition of the air trapped in the reactor is a high percentage of CO2 with some room air.

To the member who performed the experiment under high and low light conditions and reasoned that the trapped gas was O2, I'd offer the following alternative hypothesis: the increased lights also increased the temperature. As the dissolution of CO2 in water is highly dependent on temperature, less gas was could be dissolved in the reactor and collected at the top.

To combat the trapped-gas problem, I added a ball valve on the return portion of the reactor to increase pressure at this end. My reactor is designed like most others, with water entering through the very top and exiting at the bottom, both through 1/2" openings. The undissolved CO2 would bubble to the top and accumulate. The increased pressure caused by the constantly entering gas and the increasing accumulation at the top forced water out through the bottom. By adding the ball valve, the pressure on the "out" side was increased, which in turn increased the pressure within the reactor. This aids in dissolving the CO2.

In addition, I favor CO2 reactor models where the gas is introduced not at the top, but somewhere in the middle of the vertically-oriented apparatus--too high, and there isn't enough time for the bubbles to be churned in the turbulent flow; too low, and undissolved gas leaks into the return pipe.

As a final note, I'd like to add that since adding the ball valve increases pressure throughout the reactor system, the valve controlling flow of CO2 (if not automatically dosed with a pH meter) may have to be adjusted to maintain the same CO2 levels in the water.

I hope this helps.


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## NE (Dec 10, 2004)

> By adding the ball valve, the pressure on the "out" side was increased, which in turn increased the pressure within the reactor. This aids in dissolving the CO2.


I find this very interesting and probably the cause of why i never have had any issues with this and there is also a scientific ground for it as the gas dissolves better with pressure.

I have seen a big difference in dissolvement between pressure side and suction side of the pump, so the pressure part probably does not have to be that big to make a differance, so it makes sense.

I use a custom spray bar with quite small holes to get a good circulation, but i'm pretty sure it also rices the pressure in the reactor and saves me from built up gas.


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## diablocanine (Jul 25, 2004)

Might want to check with the manufacturer of your pump/filter before you choke the return, most warn against it due to premature wear and heat buildup. This coupled with too many bends in plumbing is the reason a lot of folks require a chiller...DC


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## NE (Dec 10, 2004)

What i have heard is that most manufacturers recommend that if you are going to limit the flow you should do it on the pressure side just to minimize the premature wear of the pump.


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## Fedorov (Apr 16, 2003)

Just a thought .
Why don't you put the input on the bottom and out on top ? With the out on top do not have a 90 deg turn , just go straight out . That way no gas will stay in the tube . 
Mike


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## NE (Dec 10, 2004)

Fedorov said:


> Just a thought .
> Why don't you put the input on the bottom and out on top ? With the out on top do not have a 90 deg turn , just go straight out . That way no gas will stay in the tube .
> Mike


The main cause of the reactor is to dissolve the gas into the water, thats done by letting the water flow through the gas in the reactor.
If you turn it up side down the gas will escape directly as the gas is lighter than the water and will not be dissolved into it.

The issue in this threed is not that there is gas in the reactor, but the rising level of gas in the reactor without the pH getting low enough.


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## jalfeld (Jun 22, 2005)

I have thought of running a piece of airline tubing from the top of the reactor to the venturi port on my water pump. This should cause any built up gas to be drawn off by the pump and re mixed into the water stream. I am thinking of doing this as an experiment to see if efficiency increases in the process.. Any thoughts?


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## Chris S (Feb 27, 2006)

Sounds like a good idea.I bet it does in crease the efficiency of the unit. I wanted to try this on my DIY internal reactor, but it was hooked up to the only power head in the tank and thebackpreassure created a reverse flow in the venturi. Your idea would not have worked in my case.


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## NE (Dec 10, 2004)

I don't think that's a good idea, this is why i think that,
The reactor is built for having gas inside and at some time you have gas standing at the top without it being bad, it just takes some time to dissolve all, this of course depends on plant mass and bubble rate, but more or less.
If you run a hose to the venturi you will always suck the co2 out of it and reduce the dissolvement a lot, I think this will make you a mist reactor and minimize the function of the regular reactor, more or less.


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