# Best CO2 Diffuser (with HOBs?)



## FlyingHellFish (Nov 5, 2011)

Xenxes! When did you cross over to Co2? Got a picture of your setup?

For the HOBs and Co2 levels, I didn't find a huge difference between them and canister for small-medium tanks. 

Here my Fluval Diffuser in the Edge, it's placed under the HOB.








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When I added a HOB (Aqueon Whisper) to my 60P, it didn't make a huge difference either. Try a normal diffuser first, I think you will be fine.


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## burr740 (Feb 19, 2014)

If you have an Aquaclear HOB, _that_ is the best diffuser - reactor level efficiency. Use a small piece of chopstick or piece of cotton ball in the end of the line to pre-diffuse the co2 into smaller bubbles, then run it directly into the intake.












Regular cartridge type HOBs are not as efficient due to the open water chamber in the back, co2 can off-gas right there.


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## Verivus (Jan 6, 2015)

burr740 said:


> If you have an Aquaclear HOB, that is the best diffuser - reactor level efficiency.


I see you have a sponge prefilter on the intake. Did you modify the intake somehow for the co2 line? I have an AC110 and was wondering what I should do to bypass my sponge prefilter, which is why I ask.


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## burr740 (Feb 19, 2014)

Verivus said:


> I see you have a sponge prefilter on the intake. Did you modify the intake somehow for the co2 line? I have an AC110 and was wondering what I should do to bypass my sponge prefilter, which is why I ask.


I just drilled a hole in the side of the AQs intake tube where you see the arrow (in the above pic). The co2 line is sticking through that, about halfway in. It's not fastened or anything, can easily pull it in and out. 

To begin with I had it like this for a while, which worked fine but was somewhat of an eyesore.


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## Verivus (Jan 6, 2015)

Cool, thanks! I think I'm going to do this at least until I bother putting together a reactor for my Eheim. Your impeller is still fine? That's my main concern if I did this long term.


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## burr740 (Feb 19, 2014)

There's no visible affect going on 10 months now


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## lksdrinker (Feb 12, 2014)

burr740 said:


> I just drilled a hole in the side of the AQs intake tube where you see the arrow (in the above pic). The co2 line is sticking through that, about halfway in. It's not fastened or anything, can easily pull it in and out.
> 
> To begin with I had it like this for a while, which worked fine but was somewhat of an eyesore.



I've been thinking about this all wrong! I assumed the best bet was to have an in tank diffuser directly under the intake of the AC HOB filters. I might just have to try this method and see what I get. Any difference between using the cotton vs the chopstick in the end of the line?


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## burr740 (Feb 19, 2014)

lksdrinker said:


> I've been thinking about this all wrong! I assumed the best bet was to have an in tank diffuser directly under the intake of the AC HOB filters. I might just have to try this method and see what I get. Any difference between using the cotton vs the chopstick in the end of the line?


Not much as far as the size of the bubbles, chopstick is a little finer. Of course with cotton it all depends on how tightly it's packed. The tighter you pack it, the finer the bubbles, but also the co2 line starts to bulge. This could be a problem if you've drilled a specific size hole.

The chopstick fits nicely










In my experience it's not even necessary to get the absolute finest bubbles possible at this stage. I ran a wide open line for a while. AQ20 on a 20H, co2 in the 2-3 bps range The dissolution was still almost 100% - not quite, a few microbubbles did manage to escape - but the biggest thing was the noise. There was a distinct "chirp" sound every time one of those big bubbles hit the prop. With it pre-diffused the noise goes away. There is only a very slight steady "fizz" sound that you have to get right up next to to hear.



Edit: Fwiw here's a cotton ball from when I was using a powerhead on another tank before switching to a reactor


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## xenxes (Dec 22, 2011)

FlyingHellFish said:


> Xenxes! When did you cross over to Co2? Got a picture of your setup?
> 
> For the HOBs and Co2 levels, I didn't find a huge difference between them and canister for small-medium tanks.


Hah I'm testing the waters  I want faster growth in a few tanks so I can better accommodate some slower species. Nothing setup yet, don't know what I'm doing. 

I'm going to try to build one myself for the 90g (bought a Victor SGT500 and an Ista Turbo Reactor), I still need a solenoid, needle valve, and whatever fittings. Also still need a 10 or 15lb cylinder (whatever is <26.5" tall).

AlanLe is building me another one hopefully with a dual output for my outdoor 2x 55gs powdered by a 20 pounder. But I need a diffuser solution for these, each has 2x AquaClear HOBs (30 and 50).



burr740 said:


> If you have an Aquaclear HOB, _that_ is the best diffuser - reactor level efficiency. Use a small piece of chopstick or piece of cotton ball in the end of the line to pre-diffuse the co2 into smaller bubbles, then run it directly into the intake.
> 
> Regular cartridge type HOBs are not as efficient due to the open water chamber in the back, co2 can off-gas right there.


This would be awesome since I don't have to buy anything else. I saw this on a thread before, but I read the OP said he had issues with de-gassing and it was only temporary? Moreover, the tops of my AquaClears are not covered, they're planted, and there is a bit of splashing from the output waterfall. Do you not find that an issue?


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## BanzaiJoe (Dec 23, 2014)

I went with a mist airstone inside of the AC intake. Was fairly simple to do and looks cleaner IMHO.









I have since replaced the two 90 degree fittings with a single piece of rigid plastic airline bent into a Z shape. So this is less visible and more reliable than the two fittings I was using. 

The idea here was to inject the bubbles as far away from the impeller as possible to allow for more CO2 contact with the water before even reaching the filter.


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## rick dale (Feb 26, 2014)

*diffusion*



BanzaiJoe said:


> I went with a mist airstone inside of the AC intake. Was fairly simple to do and looks cleaner IMHO.
> 
> 
> 
> ...


Does the air going directly into the hob intake , cause any gurgling noise , or any kind of noise ?


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## xenxes (Dec 22, 2011)

That does look very clean!

Is it true that feeding CO2 directly into the intake shortens the lifespan of the filter impeller?


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## BanzaiJoe (Dec 23, 2014)

rick dale said:


> Does the air going directly into the hob intake , cause any gurgling noise , or any kind of noise ?


As long as the bubbles are fine enough there is no noise. When I had the two 90 degree elbows I had a leak around the tubing that let out bigger bubbles. When that happened you could hear just a bit. This was audible only while standing directly in front of the tank. But with that issue resolved and only finer bubbles from the mist airstone there is no noise from the CO2 going into the impeller.

Bump: I've only been running this setup for a week so I can't provide any feedback about longevity based on any real world experience. But my guess is that it would be a non-issue based on quiet operation. If you heard a lot of gurgling then I would wonder more about the long term impact.


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## burr740 (Feb 19, 2014)

xenxes said:


> This would be awesome since I don't have to buy anything else. I saw this on a thread before, but I read the OP said he had issues with de-gassing and it was only temporary? Moreover, the tops of my AquaClears are not covered, they're planted, and there is a bit of splashing from the output waterfall. Do you not find that an issue?


Mine isnt covered either. The reason there's no off-gassing with AQs is by the time water reaches the upper stages of the media, and then the outflow, the co2 is already dissolved. Unlike other HOBs where the the micro bubbles leave the prop and go to the open water chamber behind the media cartridge, where they can pop at the surface before dissolving. 

Re the splash, like with any co2 enriched tank, any splash is going to off gas some co2. But here again, since the co2 is already dissolved, having a splash at the outflow shouldnt affect things any more than the same splash would if you were diffusing the co2 somewhere else. At least that's what seems logical to me. 

The tank I posted is a 20H with an AQ20, at 2bps PH drops 1.1. So I'd say off gassing is minimal regardless.


Couple things to look out for:

If you have the AQ's flow cut down all the way, or most of the way down, a co2 bubble tends to collect in the rear elbow of the intake tube. It happens on my AQ20, and another member said his AQ70 did the same thing. (it was BonzaiJoe up there I believe) So it works best to have the filter wide open, or close to it.

Not sure how much media you have with the planters, but it plays a vital role in capturing the micro bubbles so they can dissolve. Dense plant roots may do the same thing, Im not sure. But count on needing at least a sponge or two and maybe the rings for adequate diffusion.




xenxes said:


> Is it true that feeding CO2 directly into the intake shortens the lifespan of the filter impeller?


Im going on 10 months with mine and there is no noticeable affect.



BanzaiJoe said:


> I went with a mist airstone inside of the AC intake. Was fairly simple to do and looks cleaner IMHO.
> 
> 
> 
> ...


That looks so clean. :thumbsup: Im about to upgrade to an AQ30 because I need the 20 on another tank. May try something similar on the new one, probably wont do the double strainer thing. I was thinking about a piece of rigid running straight down from the top. Sealing it off could be a problem though. One good thing about the way I have it now is it's very easy to remove when you wanna clean the filer. Just pull it out of the hole and stick it back in.....very convenient. So that's something else to think about.


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## klibs (May 1, 2014)

BanzaiJoe said:


> I went with a mist airstone inside of the AC intake. Was fairly simple to do and looks cleaner IMHO.
> 
> 
> 
> ...


That looks pretty legit. I would definitely do something like this if I ran CO2 on my HOB tank


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## xenxes (Dec 22, 2011)

Well thanks, straight into the intake it is! I'd like to do something like BanzaiJoe's but doubt I'm that crafty. I guess drill a little hole on the side of my intake tube since I have a SS prefilter.


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## BanzaiJoe (Dec 23, 2014)

burr740 said:


> Couple things to look out for:
> 
> If you have the AQ's flow cut down all the way, or most of the way down, a co2 bubble tends to collect in the rear elbow of the intake tube. It happens on my AQ20, and another member said his AQ70 did the same thing. (it was BonzaiJoe up there I believe) So it works best to have the filter wide open, or close to it.
> 
> That looks so clean. :thumbsup: Im about to upgrade to an AQ30 because I need the 20 on another tank. May try something similar on the new one, probably wont do the double strainer thing. I was thinking about a piece of rigid running straight down from the top. Sealing it off could be a problem though. One good thing about the way I have it now is it's very easy to remove when you wanna clean the filer. Just pull it out of the hole and stick it back in.....very convenient. So that's something else to think about.


I have my AC70's flow down to the minimum. No issues in doing so. I think it was one other poster that mentioned an accumulation of CO2.

I never thought about running the rigid line straight down from the top. You'd definitely have to seal it but it could easily be done with some silicone sealant if you really wanted to. But the line might get in the way of putting the lid on the filter if you run one.

The intake extension for that AC70 is just another section with the strainer. You basically get two identical strainer tubes. So I drilled out the center of the upper one instead of just cutting the extra strainer out. The added bonus is that it holds the line centered inside the intake tube.
The whole assemble comes apart and goes together pretty easily so access for any maintenance is simple.


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## BanzaiJoe (Dec 23, 2014)

Here is a pic with fittings replaced with rigid tubing. That was way easier than dealing with the fittings in addition to being more reliable.









The only tools you'd need are a drill for the hole in the intake and a lighter to heat up the rigid tubing to bend it in shape.


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## xenxes (Dec 22, 2011)

Thanks for the new pic!


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## BanzaiJoe (Dec 23, 2014)

An important note is to make that drill hole below your water line unless you are going to completely seal it or else you'll draw air into the filter.

Maybe not quite as clean, but you could easily have just drilled out the center of the strainer and fed your line up from the bottom. Could also pop on a small airstone too.


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## burr740 (Feb 19, 2014)

So I upgraded to the AQ30 and trying out a different way to do it. Instead of using the intake, using the aeration hole in the removable plate that sits just above the impeller. It's a perfect fit.





















Once installed there's not enough clearance to use a piece of chopstick, so I went with a piece of cotton ball...




















CO2 @ 2.3 bps (23 per 10 secs) There are zero bubbles in the outflow and it's dead silent..


Two possible downsides: The aeration hole is there for air to escape during start up. With that now plugged, the filter will no longer start itself dry. Gotta fill it up first, which I always do anyway. The other thing is obviously now the lid wont fit. So you'll have to make a cut out for the tubing if you want to use the cover.


**** Disclaimer: Just set it up so I havent had a chance to test the PH drop yet to see exactly how efficient this is. Before I was getting a solid 1.1 drop. Also noticing a stray bubble or two emerging in the water chamber. That may be CO2, Im not sure. Could be from the brand new ceramic rings or something. I will report back when I know for sure in a couple days. Really hope this works.......


Edit: Those bubbles were definitely CO2, but I think it's fixed now. If you have one of these in front of you, you'll notice the plate sits up about 3/4 of an inch above the impeller. To begin with I had the CO2 line pulled up as high as it would go (the cotton ball swells the tubing so you cant pull it all the way back out). There was zero sound, and a fairly big bubble coming up from the impeller side of the media...one or two about every 30 seconds. What I did was reach in and push the co2 line all the way down until it hit bottom. Soon as I did that it started to make the little "sizzle" noise like it used to. That told me the micro bubbles were being drawn into the prop. Since then no more bubbles. 

I had already decided if it didnt work I was going to try drilling a new hole on the opposite side of the plate. That would put the co2 entering more behind the impeller, rather than beside/in front of it like it is now. I still think that would be a good move, but it may prove unnecessary because it seems to be working fine now. I'll post some definite results in a day or two...


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## quiquik (Dec 13, 2013)

Yes Burr 740 I remember discussing this in another post. The hole is perfect for the tubing and I'm wondering if using a piece of chop stick would be better than cotton, at any rate this is the way I believe I will do it on mine when I get the rest of what I need to redo my 50 gal. I'm also contemplating splitting my co2 tubing to run to both of my AC 70's for more even distribution or do you think that would not be necessary? The system will be pressurized not diy co2.


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## burr740 (Feb 19, 2014)

The problem I _assumed_ with a chopstick, is it would have to be a very short piece. But since it appears that whatever is used needs to reach the bottom, Im thinking a 3/4" piece would work, with maybe 1/4" inside the tubing and 1/2" sticking out. I used to slope the ends of mine on an angle, so that may also come in useful. 

Another thing I thought of, after seeing the line needs to go all the way down, is running it on through about 1 1/2" or so, and letting it fold 90 degrees toward the outside (hopefully with no kink). That would put the end over where I was talking about drilling a new hole, and could also allow for a longer piece of chopstick if you choose to use that instead of cotton.

Re dividing it up between two filters, that would be ideal with each one doing half the total bps....probably a big difference between 10 bps and 5 for example. Also there'll be a more even dispersion of co2 throughout the tank coming from two different areas vs one.

------------------

12 hours later still no bubbles coming from either the water chamber or the outflow, so looks like it's gonna work. Im waiting on a bowl of tank water to fully degas to do a PH test.


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## quiquik (Dec 13, 2013)

Yes it seems that there may be enough room to push the tubing in and not kink, that way like you said the co2 is in front of the impeller being drawn through it and not behind it just being push right away into the media chamber.


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## BanzaiJoe (Dec 23, 2014)

burr740 said:


> So I upgraded to the AQ30 and trying out a different way to do it. Instead of using the intake, using the aeration hole in the removable plate that sits just above the impeller. It's a perfect fit.


 That could make for a clean install as there is nothing visible in the tank.

But I wonder what if any difference there is in injecting the CO2 right at the impeller vs. further upstream in the intake. Insignificant, or something that makes it worth putting the injection point upstream.


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## benealing (Jan 9, 2015)

So, I am the one that had the air bubble in the intake elbow. Today, when I did my water change, I followed this plan. In order to have the lid fit on, I just threaded the CO2 tubing through the hole in the lid that allows flow control. This works out great. I like not having tubing inside the aquarium. I also like not having an air bubble in my intake. 

As a side benefit, the airline tubing sitting through the flow hole, allows me to reduce the flow by about 33% and keep it there. The air tubing will not allow the flow to be fully reduced.

I have significantly less CO2 bubbles coming out of the filter now and my pH dropped incredibly fast post water change. Seems like a winner to me.

Thanks for your novel thinking!!

Ben


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## burr740 (Feb 19, 2014)

That's good to hear, benealing. I didnt even think about using the flow control hole in the lid.


PH tests:


De-gassed tank water












With the tube going straight in the hole (pushed all the way down)











With the tube pushed through further, and folded over so the output is more behind the impeller. (silicone tubing wont kink, not sure about vinyl)



















Tube running straight into the intake...virtually the same


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## bwhupp (Apr 1, 2015)

I am debating on CO2 since I got a hair algae growing on my low light tank. This is great information as I run an aquaclear70 on a 20 Extra High tank.


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