# CO2 Diffuser Placed Below Filter Intake?



## skoram (Aug 9, 2012)

I just ordered my first high-pressure CO2 system and am trying to decide on the ideal location for my diffuser. 

I'm using an Eheim 2217 on a 30 gallon tank with glass lily pips both on the right side. I thought about placing the diffuser somewhere below the outlet but concluded that this would only be beneficial if it is placed *directly* below the outflow - impossible without positioning the diffuser 4 to 5 inches away from the glass. 

My second thought was to place the diffuser near the intake tube. Since the tube is positioned much closer to the glass and it is sucking in water, I believe a large amount of the CO2 should be captured before reaching the water surface. 

Has anyone ever tried this? Are there any negative consequences that could result from this positioning?


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## TwoTacoCombo (Apr 13, 2012)

Have you looked into an inline diffuser/reactor instead? I use an Ista Max Mix reactor to inject the CO2 straight into the filter's water stream. No bubbles ever reach the outlet of the filter system, so not a whole lot is wasted.


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## chew (May 18, 2012)

The co2 will eat away at your impeller on your filter. My eheim also got gas pockets inside the filter every few minutes and it would get louder. You can always try placing it opposite side of your outtake. When I go to AFA a lot of theirs have it set up like that


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## pwolfe (Mar 2, 2011)

another option is in line diffusers


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## thinBear (Dec 16, 2011)

how abt place it at the opposite of the outflow, so as the bubble raises it 
"rubs" against the down current.

I'd take external or internal CO2 reactor, if aesthetics is not a main concern.


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## skoram (Aug 9, 2012)

Thanks for the replies everyone. Unfortunately I do not have space for a big reactor. I thought about the inline atomizer/diffusers, but I got the impression that they make your tank look "fizzy" from all the tiny bubbles being sprayed in. 

Ideally, I want to balance aesthetics with good functionality. The CO2 doesn't have be 100% dissolved but more dissolution is of course better.


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## Jeff5614 (Dec 29, 2005)

Placing the diffuser near the filter intake is worth a try if you want to minimize the mist floating around in the tank. You're going to hear a lot of people tell you that it will damage the impeller or the gaskets in the filter, but I would be willing to bet none of those could provide you with an actual example of that happening. You'll also hear the argument that it will suppress the biofilter. I can understand both sides of that discussion but haven't seen actual evidence supporting either. As long as you're not injecting so much CO2 that it's accumulating at levels much higher than what you're going to have in the tank, then I don't see how either of those scenarios are any different than the affect of having the CO2 enriched water from you tank circulating through the filter.

From what I've read from people who do diffuse CO2 through their filter, the issue some have is with the filter burping because they're adding CO2 at such a rate it accumulates in larger bubbles which finally work their way out.

I use a diffuser in my 75g and prefer to place the diffuser on the opposite end of the tank from the filter output, ala ADA. The current pushes the CO2 around the tank in a circular motion and since it's carried around the back first, the mist has pretty much dissolved by the time it makes it to the front of the tank so there's very little of that misty look in my tank.

If you do some reading on UKAPS.org, you'll find injecting CO2 into the filter a bit more common practice among those members than here on TPT so you might get a bit more insight there.


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## PlantedTankRookie (Feb 21, 2013)

I use the fluval ceramic diffuser and I have it mounted directy below the suction line of one of my two 2217s. All of the CO2 I can see gets sucked into the filter. I never see any bubbles coming out of my filter output. I run enough CO2 to drop pH from 7.8 to 7.0 (green green on my drop checker) in a 125 gallon tank. I run CO2 6 hours per day (two 3 hour periods).
I could easily get more CO2 in the water (I've been well into the yellow with this setup).
Both of my 2217s are still as silent as when they were new but they are only 3 and 4 months old.


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## talontsiawd (Oct 19, 2008)

skoram said:


> Thanks for the replies everyone. Unfortunately I do not have space for a big reactor. I thought about the inline atomizer/diffusers, but I got the impression that they make your tank look "fizzy" from all the tiny bubbles being sprayed in.
> 
> Ideally, I want to balance aesthetics with good functionality. The CO2 doesn't have be 100% dissolved but more dissolution is of course better.


It seems everyone has a different experience with inline diffusers. Even with the GLA ones, some say they can't see any bubbles, some say they have bubbles everywhere. For me, I see a few bubbles coming out at the intake nothing really bothersome. I am guessing it's different when you use lily pipes vs. a spray bar. 

As for an in tank, I haven't had an issue having it almost anywhere in the tank, as long as you have enough flow. Again, usually using lily pipes, I tend to put the intake and outflow on one side of the tank, the diffuser on the other and that works well for me. I don't like putting it under the intake as it makes my filters noisy.


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## skoram (Aug 9, 2012)

Thanks for all the good info. I've looked at a few other threads about inline diffusers and it seems that, as talontsiawd pointed out, results can vary quite a bit. I'm willing to bet a lot of the "fizziness" has to do with how close you position the diffuser to the outlet. 

Perhaps I should make another thread about this, but one concern I have about inline diffusers is that it seems they require a much higher psi (people have said around 40) to operate properly. I'm totally new to high-pressure CO2 so forgive me if this is a dumb question, but won't setting the output to a much higher psi cause the cylinder to empty much more quickly? The cylinder I ordered is pretty small (1L/0.98 kg) since I have very limited space around my tank.


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## skoram (Aug 9, 2012)

Based on everyone's feedback I decided to do a little more searching and finally purchased an Ista External CO2 Ceramic Reactor. You can find plenty of pics by doing a google search. It's a very small inline unit so I didn't have to worry about having another big bulky canister, and since it's a reactor and not a diffuser, I thought I wouldn't have to worry about the soda pop appearance or or all the other issues that people have had (cleaning problems, leaks, etc.) with the inline atomizer. I can say that it is very convenient, easy to set up and seems to work fairly well. However, unlike what I assume is the case with the big reactors, this shoots quite a lot of tiny bubbles into my tank and the end result seems to be almost the same as having an inline diffuser. Overall I'm fairly happy with the product but slightly disappointed that it seems far from a "true" reactor in terms of effectively dissolving all CO2. As you can see from the pic below, there is a very short distance between the reactor and my output pipe, so results will probably differ for those who have more line between the 2.


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## blink (Feb 22, 2012)

I have an all-in-one cube tank so the filtration is a little different, going through the rear chambers, then out a return pump but I've had my CO2 diffuser directly under my pump intake since January with zero evidence that it's done any damage to the impeller and no escaping bubbles, nor any visible bubbles in the water which is what I was really hoping to accomplish.

I would try it under your intake and see what happens, if the worst case situation happens and it does damage your impeller, well then you move it to a different place and buy a new impeller for $10-15.


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