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Old 02-15-2005, 12:14 PM   #1 (permalink)
 
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Default Pondering pressurized CO2...

Ok, after seeing the response from Trena in another thread about the incredibly inexpensive CO2 regulator, I have a question.

Can someone give me a rough idea of how long a bottle of CO2 will last? For the sake of discussion, let's assume a 5 pound bottle, with no solenoid/controller. Yes, I know it hinges on bubbles per minute, so let's add some more parameters...

55 gallon tank, Emperor 400 filter. Air curtain at the back of the tank (non-negotiable - my wife said so!) Hagen bubble ladder, fed by Tygon tubing (essentially impermeable to CO2). (I'm going to be building a wet/dry filter, and have designed in a powered CO2 injector in the sump, just before the return pump, for more efficient dissolution. Let's leave that out of the equation for now.)

When the DIY twin-2-liter setup works (it's "between batches" now - I screwed up the setup last weekend - sigh!) the plants apparently get some sort of benefit from the CO2, despite the air curtain - better color, phenomenal growth, etc. There isn't an appreciable impact on pH, though this tank is kept at pH6.5, and the kH is only about 0.75 degrees. The bubbles hit the Hagen ladder at a rate of probably 8-12 per minute, and dissolve almost completely before they hit the top of the ladder. I've stuffed a shaped piece of foam at the top of the ladder to catch the remaining bubbles and give them more chance to dissolve further.

Again, for the sake of discussion, let's assume I keep the bubble rate at 12-ish per minute, 24/7. How long should a 5-pound bottle last me? Translated, how much will it cost long term - I may be able to convince my wife to let me get a <$100 setup, unless it'll cost $50 a month for CO2 - ale yeast and sugar are cheap!

Thanks for your help!

Glen
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Old 02-15-2005, 12:27 PM   #2 (permalink)
 
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Hey Glen,

I run mine at 2-3 bubbles per -second- 24/7 and a 5 pound CO2 tank lasts about 4-5 months. Get it refilled at Airgas up on North Lamar near Braker and it costs about $12 to refill. Buy the tank there and just swap it out each time you refill.

TW
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Old 02-15-2005, 02:27 PM   #3 (permalink)
 
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Hey, TW, thanks!

Not only a specific response, but one from a local with local prices!

I really appreciate it - heck, at less than $3 per month, that's not much more than ale yeast and sugar.

Glen
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Old 02-15-2005, 03:38 PM   #4 (permalink)
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I have my 5lb C02 setup on my 55G tank for 2 months now with no drop in pressure and I'm running at 3 bubbles per second. From what I have read on forums any where from 4-12 months is normal, depending on the size tank, size cylindar and bubbles per second.



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Old 02-16-2005, 01:42 AM   #5 (permalink)
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I would seriously consider raising your KH a bit: up to 3 or 4.

A KH of 0.75 while injecting CO2 risks causing a pH dive...
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Old 02-16-2005, 05:36 AM   #6 (permalink)
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Great catch, Laith!



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Old 02-16-2005, 05:50 AM   #7 (permalink)
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With a bubble wand in the back you're going to be blowing off most of the CO2 you put in there. Seachem Excel would be a better route for you to go. There's no point in spending the money on gas that's not going to work too well.

Best,
Phil
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Old 02-16-2005, 06:32 AM   #8 (permalink)
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In addition to the bubble wand that Phil mentioned, you are also running an Emperor 400 with dual bio-wheels. That is going to contribute to even more off-gassing of CO2, unless you remove the bio wheels. I don't know how much off-gassing, but between the two (bubble wand and Biowheels) you will loose a lot of CO2.

Ever thought about hooking the CO2 to the bubble wand? I'm not sure how well or if it would work but it shouldn't cost you anything to give it a try.

I would personally remove the bubble wand and Emperor if I went with CO2. Since that isn't an option in your case, you can probably expect to go through a lot more CO2 than TWood does.
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Old 02-16-2005, 08:17 AM   #9 (permalink)
 
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Ok, everyone, thanks for the input. More discussion follows; I'd appreciate further analysis:

The pH is stable at 6.5-6.6 with the kH at 0.75 with (or without) the DIY CO2 setup I have. I figured that if I went with a "real" CO2 system I'd introduce it gradually and adjust the kH if necessary. With the tank as it is now, if I increase the kH even a tiny bit (with either Seachem Alkaline Buffer or baking soda) the pH shoots into the mid 7s. If someone has an idea how I can keep the pH in the mid 6s, while simultaneously increasing the kH, I'd love to hear it. We do ~30% water changes every week, and (knock wood) so far things have held pretty steady. From the charts, it looks like my max kH in a non-aerated system would want to be around 2-2.5 to stay around 20-25 ppm CO2 at a pH of 6.5 - I doubt that kind of balance is achievable with an aerated system.

The Emperor is basically a requirement until I get the wet/dry built (not to start another holy war about the evils of a wet/dry in a planted tank, either...) Injecting the CO2 just before the return pump in the wet/dry will give it the best start at providing a benefit. My wife considers this to be a fish tank with plants, so we have a really heavy bioload (nearly 1.5 inches per gallon). The nitrate levels are holding steady at 5-10 ppm - in fact, I'm probably going to have to add KNO3 to my PMDD once the plants grow a bit more to keep them above 5 ppm.

I didn't know that the Seachem Excel provided bioavailable carbon - I'll get some and see what it does. I take it that (from y'all's experience) it's more than snake oil? (Yes, I know Seachem frequents the forum - that's supposed to be a funny, 'k?) Seriously, what kind of benefit have you seen from it?

I've seen what the plants do with the DIY CO2, and it was pretty amazing. Frankly, I hadn't expected much due to the aeration, but apparently any CO2 is better than none. I think I'll try the Excel while the yeast is "between gigs", then crank up another batch of CO2, and see what's what. If nothing else, it'd be an interesting experiment.

Once again, I appreciate the input, and I'll post results as things progress.

Glen
Eschew misoneism.

Edit:
I'd thought about injecting the CO2 into the bubble wand, but can't think of a viable way to do it, especially with DIY CO2. The back pressure from the air pump might overload the CO2 system; with a bottle, the back pressure from the CO2 might overload the air pump. I may ponder that idea further - it's a deep-water air pump, so it may not pose a problem...

Last edited by glenhead; 02-16-2005 at 08:27 AM..
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Old 02-16-2005, 09:48 AM   #10 (permalink)
 
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Okay, just got back from Airgas and this time a 5 lb refill was $9.34. Why does the price of CO2 vary? Volume of cow farts? No, that's methane....

Anyway, that KH figure does seem low. Mine sets in at 2-3 using the el cheapo Aquarium Pharm test kit. To get the KH at that level and pH below 7, it just takes more CO2. Figure about 1 bubble per second per 40 gallons of water.

Ah yes, the wife factor... One of our tanks has a bubbling drunk skeleton because of that variable. Just set the air pump to the lowest volume you can get away with. Some CO2 -is- better than none, so if you are stuck with the air curtain, so be it.

BTW, if you haven't shopped Aquatek on Burnet Road, they have the best plants in town.

TW
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