Kordon breather bag as CO2 diffusion device? - The Planted Tank Forum
 
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post #1 of 8 (permalink) Old 06-14-2006, 09:03 PM Thread Starter
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Kordon breather bag as CO2 diffusion device?

I was bagging up some shrimp for someone today, and something occured to me. I'm wondering if it's been discussed before.

Kordon breather bags are designed to hold in water, but allow gasses like O2 and C02 to pass through their walls. So if someone attached a bag to their CO2 airline inside their tank (with a rubber band or a hose clamp maybe), would it effectively become a diffusion "balloon"?

I haven't actually tried it yet, but I imagine these might be the pros and cons:

Pros:
- cheap and replacable (vs. what it costs when a ceramic disc goes bad)
- many sizes available, and even the smallest size could be cut down further
- can be positioned upright, on its side, maybe even half-buried (provided you have something to hold it down)
- 100% diffusion (?)

Cons:
- holding it down
- requires a very good way to get a seal around the airline to prevent leaks
- could pop (?)
- weird-looking
- rumor that these bags have been discontinued (there might be other brands, I'm not sure)

What I'm wondering is what happens when the pressure builds up. Does it help force gas through the bag faster? Will it cause it to stretch enough for streams of little bubbles to pour through? Will it break?

Since I haven't tried it, the bubbles may come out visibly no matter what for all I know. Certainly not a replacement for better diffusion techniques out there. Just putting the idea out there.

Last edited by endparenthesis; 06-14-2006 at 11:29 PM.
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post #2 of 8 (permalink) Old 06-15-2006, 01:46 AM
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I googled Kordon and read about the breather bags. I doubt that they will work as diffusors. You should note that if you fill the bag with oxygen the oxygen will stay there for several days. This tells me that the rate of diffusion of gases thru the bag material is very, very low, which is fine for its intended purpose. Fish don't use a whole lot of oxygen. So, to make this work as a CO2 diffuser, you would probably need many, many square inches of bag, possibly a bigger bag than the fish tank!

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post #3 of 8 (permalink) Old 06-15-2006, 02:08 AM
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Breather bags are made to work as a permeable membrane with one side being water and the other being air. How long it lasts filled with air does not matter. It would matter only if the bag was submersed under water. But I do agree that it probably would not work.


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post #4 of 8 (permalink) Old 06-15-2006, 02:08 AM
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Hoppy I don't think this is how the breather bags work. At least the ones I am familiar with... you are supposed to fill them completely, without air, and then the CO2 excess in the water is supposed to exchange through the bag and be replaced with O2 from the surrounding air. That won't work for shipping Labyrinth fish of course.

As for CO2 diffusion devices... haven't tried it, and I think there are better looking things out there. But why not try it if the looks aren't what you are after? (a ladder might work better though... on a long term)


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post #5 of 8 (permalink) Old 06-15-2006, 02:16 AM Thread Starter
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Guess this is why I haven't heard about it being done before. Good to know.
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post #6 of 8 (permalink) Old 06-15-2006, 05:44 PM
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I hope someone does try using those bags as diffusers. Everything we learn and share does help us all. Just because the bags are not likely to work is no reason not to try them. After all, allowing GDA to live out its life cycle wasn't likely to work either, but it does.

One more thing about the breather bags. They allow molecules of gases to pass thru, not bubbles. So, you wouldn't expect to see anything happening if you used one as a diffuser, except the lower pH. But, I still doubt that enough molecules would diffuse out to give enough CO2 to be of benefit - they are intended to diffuse out fish respired CO2, which is a very minute amount, and diffuse in the oxygen needed by fish, also a minute amount.

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post #7 of 8 (permalink) Old 06-15-2006, 05:57 PM Thread Starter
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I guess if the CO2 has been running for a week and the bag isn't leaking or broken, it's safe to say it works. There's nowhere else for the CO2 to have gone but the water (assuming a leak-free setup).
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post #8 of 8 (permalink) Old 06-15-2006, 06:13 PM
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Quote:
Originally Posted by Wasserpest
That won't work for shipping Labyrinth fish of course.
Good point...don't ship Corydoras using these bags in that manner either as they also need the air pocket.

I think the diffusion rate would not be fast enough using the bags this way. My guess is that it would pop under the pressure first.


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