Is this normal from a DIY reactor? - The Planted Tank Forum
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post #1 of 20 (permalink) Old 06-27-2011, 10:01 PM Thread Starter
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Is this normal from a DIY reactor?

I just installed my DIY Rex Griggs style reactor and noticed that i was getting a decent amount of large bubbles out of the ouput. They werent huge, but large enough to immediately float to the surface and offgas. I tilted it to the side a little bit and it helped a lot, but i still get some larger bubbles on occasion. Has anyone else experienced this?

The reactor is 2" in diameter and 22" long, running off of an XP3 filter. It doesnt have any media in it, just good old fashioned physics.

I hope this is in the right section. If not then i apologize.
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post #2 of 20 (permalink) Old 06-27-2011, 10:24 PM
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Did you turn it upside down to purge all the air out of it before turning the CO2 on. During initial setup they will have alot of air in them till they get purged.

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post #3 of 20 (permalink) Old 06-27-2011, 10:37 PM Thread Starter
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I dont quite understand what you mean by turning it upside down?

I filled it with water and got as much of the air out as possible before i ever turned the filter on. Then i let it run for 4hrs to make sure it was water tight before starting the co2. It took probably an hour and a half for it to purge all of the air, but it ran for hours without any bubbles before i turned on the co2.
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post #4 of 20 (permalink) Old 06-27-2011, 10:39 PM Thread Starter
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The reactor is pretty loud now. Im thinking whats happening is that since its at an angle(and the inlet is no longer the highest point) the co2 is pooling at the top of the reactor and slowly getting absorbed into the water. This is probably a more effecient way of diffusing it so im not going to worry about it unless i find any other problems.
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post #5 of 20 (permalink) Old 06-27-2011, 10:54 PM
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Originally Posted by sceraxn View Post
The reactor is pretty loud now. Im thinking whats happening is that since its at an angle(and the inlet is no longer the highest point) the co2 is pooling at the top of the reactor and slowly getting absorbed into the water. This is probably a more effecient way of diffusing it so im not going to worry about it unless i find any other problems.
...that's how they work and why people make them
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post #6 of 20 (permalink) Old 06-28-2011, 12:03 AM Thread Starter
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...that's how they work and why people make them
Im not sure thats quite accurate. If its vertical like most people have them then the inlet is the highest point and the co2 wont really have a chance to pool. The constant recirculation of the co2 bubbles will slowly break them down until theyre small enough to be carried away by the flow of water. The other reactors ive seen are usually pretty quiet, but they were always perfectly vertical instead of at an angle like mine is so the co2 couldnt puddle at the top. Mine quiets down when i put it straight up, but then i start getting larger bubbles out of the outlet, so ill just deal with the noise if it means better diffusion.
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post #7 of 20 (permalink) Old 06-28-2011, 03:35 AM
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When you say inlet, is it the CO2 inlet? My reactor usually gets louder when the bubble count is high since the CO2 isn't being absorbed fast enough.


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post #8 of 20 (permalink) Old 06-28-2011, 05:58 PM Thread Starter
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When you say inlet, is it the CO2 inlet? My reactor usually gets louder when the bubble count is high since the CO2 isn't being absorbed fast enough.
I meant the inlet where the water comes in from the filter. If it isnt the highest point in the reactor then the co2 will pool easier. Ive got it at an angle now so that the co2 can pool, which seems to allow it to diffuse into smaller bubbles and it seems to have a more consistant diffusion rate.
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post #9 of 20 (permalink) Old 06-28-2011, 10:35 PM
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I believe this may have something to do with your filter, it's too powerful. I have the same length and size PVC for my reactor but I'm only using an XP2. You can always add a few more inches to the PVC with a coupler. This will give your CO2 enough time to travel up and pool for maximum contact. This way you can keep your bubble count and not have to slow down the filter.


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post #10 of 20 (permalink) Old 06-28-2011, 10:39 PM Thread Starter
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The co2 is defnitely pooling so i dont think its the flow. But youre right that it pooling seems to really help the diffusion. Its working good now that i have it at an angle, its just a little louder lol

edit- I just realized that i gave you guys the wrong measurement. I used a 22" piece of PVC, so with the two couplers its actually 25" long.
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post #11 of 20 (permalink) Old 06-28-2011, 11:19 PM
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Is the outlet at the top or bottom? I believe you want the water to flow down, against the rising CO2 bubbles. Maybe I'm misunderstanding, when it's vertical, large bubbles come out? Are the pushed down and out? That sort of does sound like too much flow.
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post #12 of 20 (permalink) Old 06-29-2011, 12:07 AM
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With a 2" diameter reactor on an XP3 you might get bubbles pushed out on the bottom. I went to a 2.5" diameter and that worked. It's not so much the length, but the diameter that slows down flow and gives the bubbles a chance to dissolve.

Regarding accumulation of gas, have you noticed this happening more in the afternoons? Or do you have the same issue in the mornings? If there is a lot of photosynthetic activity in the tank, you might get an accumulation of O2 (not CO2) in your reactor. O2 doesn't dissolve as readily as CO2 so it tends to accumulate and create some noise. There are a few things you can do to combat/minimize this... if that is what's happening.


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post #13 of 20 (permalink) Old 06-29-2011, 01:42 AM Thread Starter
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Is the outlet at the top or bottom? I believe you want the water to flow down, against the rising CO2 bubbles. Maybe I'm misunderstanding, when it's vertical, large bubbles come out? Are the pushed down and out? That sort of does sound like too much flow.
Yea the flow is from top to bottom. When its vertical larger bubbles come out, but theyre still fairly small. I just noticed that theyre a lot smaller when i tilt the reactor at an angle.

Im not really trying to troubleshoot a problem or anything though. It works really well so im not going to change anything. Just wondering if anybody else had noticed that it diffuses better at an angle. I did a little searching on here earlier today and found that a lot of people people had noticed the same thing. 5 or 10 people mentioned it in Rex's thread on how to build one.

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Originally Posted by Wasserpest View Post
With a 2" diameter reactor on an XP3 you might get bubbles pushed out on the bottom. I went to a 2.5" diameter and that worked. It's not so much the length, but the diameter that slows down flow and gives the bubbles a chance to dissolve.

Regarding accumulation of gas, have you noticed this happening more in the afternoons? Or do you have the same issue in the mornings? If there is a lot of photosynthetic activity in the tank, you might get an accumulation of O2 (not CO2) in your reactor. O2 doesn't dissolve as readily as CO2 so it tends to accumulate and create some noise. There are a few things you can do to combat/minimize this... if that is what's happening.
People have used smaller reactors on eheims with more flow than my XP3. Besides, length has more to do with how its diffused then width. Technically, if you had a long enough hose(it would need to be like 8' long lol) you could do this with the 5/8"-3/4" hose thats on your filter without needing a reactor as long as the initial bubble size was within a certain percentage of the overall diameter of the tubing. Its been 10 years since my fluid dynamics courses, but im sure i could dig up the calculations to support this, though id rather not have to dig out all of my old textbooks

The noise starts around 20 minutes after the co2 comes on, which is about how long it would take for the co2 to pool at the top. The noise doesnt change at all until maybe 15-20 minutes after the co2 cuts off(takes that long to diffuse the remaining co2 in the reactor). I dont think its o2 thats getting in the reactor. I cant imagine how it would get in there because there shouldnt be enough pressure and turbulence to cause cavitation. Before i installed the reactor i never had bubbles from that filter so i cant see why it would start now.
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post #14 of 20 (permalink) Old 06-29-2011, 02:36 AM
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I really like Tom Barr's Reactor design. http://www.barrreport.com/showthread...al-CO2-reactor He incorporates a venturi loop to automatically purge out the gasses that form at the top of the reactor. You can set the loop to the intake on your filter so the gases get sucked out by it. They then pass through the impeller on which chops them all up and recycles them back into the reactor. The gasses recycle over and over until they are either dissolved or small enough (less then .5mm) to loose their buoyancy and pass through the bottom. It seems to work well so far and is very quiet.
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post #15 of 20 (permalink) Old 06-29-2011, 02:10 PM Thread Starter
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Yea i was initially planning on using that design, but i didnt want to try and shove more equipment into my already full cabinet. If i was running any filter other than the Rena i wouldve still made it that way and just routed the venturi line back into the intake on the filter. However, i tried injecting co2 directly into the filter the first time around and it didnt like it at all. The co2 would pool inside of the filter and then it would burp it all out at once.

Im still planning on using that style of reactor on my 20l though. It does seem like the most effecient design out there, it just wasnt right for my 55 and the equipment im running on it.
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