# Co2 diffuser placed under canister filter intake?



## alsmith (Nov 27, 2013)

I've never put the co2 on the intake of the canister filter for two reasons. Firstly the high levels of co2 in the filter will severely hinder the growth of bacteria in the media. Secondly, the owner of my LFS a wise man in my view says over time the co2 causes the breakdown of plastic/ rubber which can potentially damage the filter.


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## Darkblade48 (Jan 4, 2008)

alsmith said:


> Firstly the high levels of co2 in the filter will severely hinder the growth of bacteria in the media. Secondly, the owner of my LFS a wise man in my view says over time the co2 causes the breakdown of plastic/ rubber which can potentially damage the filter.


I think the latter problem is much more of a problem than the former. 

While CO2 has an effect on bacterial growth, I would not say it severely hinders it.


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## rezco (Jan 25, 2012)

alsmith said:


> over time the co2 causes the breakdown of plastic/ rubber which can potentially damage the filter.


That too is a myth. I have a chemical process engineering background - we deal occasionally with issues of micro cavitation and chemical corrosion in industrial pumps which I assume is the origin of this myth in aquaria. In industrial applications the fluid conditions are much more demanding and hardly apply to aquaria.

To be clear CO2 is not going to cause wear of aquarium systems - there may be low pH but plastic and other components are quite chemically resistant. The other concern could be due to erosion caused by bubbles being fed into the impeller. The fluid pressure is quite low and will not impact the hard impeller blades at all. 

I searched on TPT a while ago for any first hand account for such a failure but could not find any.

I have been running my own test for 3 years by inserting CO2 tubing directly into the intake of a Magnum HOB canister with great results. Recently I started a 70 gallon - first tried CO2 fed via a 3 inch wooden airstone and the fine bubbles were circulated by directing the exhaust of the Magnum - achieved light green (~30 ppm) in my drop checker - bubble rate 3 bps.

Next I removed the airstone and inserted the tubing directly into the intake of the Magnum HOB. A light green color was obtained at 1 bps. Therefore the intake delivery system is much more efficient than diffusers.

In my opinion the CO2 dissolution takes place inside the filter in much the same way a Cerges reactor operates. Furthermore the filter impeller functions as a diffuser by chopping the incoming CO2 into fine microbubbles further enhancing the efficiency of the system.


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## chew (May 18, 2012)

I just don't like the loudness of my filter and the burps of co2


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## Texan78 (Nov 17, 2013)

I would think over time this would cause your motor to burn up in a canister filter as the gas bubbles would create air pockets. It's not good for your pump to be sucking air.


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## asuran (Oct 12, 2007)

it dependents on the canister design, some canister will trap air in a long run, and make noise. Almost all impeller diffusers will blow the co2 to the mist all over the tank. 

I personally don't like the mist and noise, A inline reactor is much better, 



Beakman said:


> Over the past couple of months I've been experimenting with the placement of my ceramic co2 diffuser.
> 
> I have 2 two liter bottles of DIY co2 on a 20 gallon tank and I'm trying to place the diffuser to get the maximum diffusion into the water. I had it placed so that it was floating up in front of the out flow of the filter which would push the bubbles back down into the water and spread them around the tank.
> 
> Then I tried placing it under the intake. The co2 goes in and every now and then the filter "burps" the gas back out. My question is if this is actually efficiently diffusing the co2 and if this would damage my filter in any way.


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## Veritas (Aug 9, 2013)

I have my co2 ceramic diffuser directly below the intake of my Fluval 405 - and it seems to do a great job of chopping up the co2 bubbles - I seldom see any leave the outtake - yet my plants have really taken off ever since I installed it! Finally getting some carpeting of my DHG!


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## DizzyD (Apr 24, 2013)

I'm glad i found this thread... I'm planing a diy co2 in my 28 Gallon and was wondering if positioning the diffuser under the filter intake would have any effect.


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## PlantedTankRookie (Feb 21, 2013)

It also depends on how much CO2 you inject into the filter. I run enough CO2 into my eheim 2217 to drop my pH from 7.2 to 6.5. If I crank the CO2 any higher I start to see bubbles in the filter discharge. I can't tell you how many bpm because I don't use a bubble counter.


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## Veritas (Aug 9, 2013)

DizzyD said:


> I'm glad i found this thread... I'm planing a diy co2 in my 28 Gallon and was wondering if positioning the diffuser under the filter intake would have any effect.


I *might* be a little more worried with DIY co2 than with pressurized, with the possibility of remnants of the yeast? 

don't quote me on that, just a thought


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## DizzyD (Apr 24, 2013)

Veritas said:


> I *might* be a little more worried with DIY co2 than with pressurized, with the possibility of remnants of the yeast?
> 
> don't quote me on that, just a thought


I am worried about the remnants even without putting it under the intake... I was thinking about having a bubble counter bottle outside of the tank just so and remnants would be left in that water instead of the tank. Not sure how well this will work but It might be worth a try...


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