10lb CO2 vs 2.5G tank? - The Planted Tank Forum
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post #1 of 15 (permalink) Old 05-03-2020, 09:31 PM Thread Starter
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10lb CO2 vs 2.5G tank?

I have a 10lb CO2 cylinder and was thinking about using it for my 2.5 nano to carpet DHG... is 10lb okay, or is it way too big/too much? I was thinking that since I can regulate it, it'll last me for a long time so it wouldn't be that bad to use it. Was looking for opinions and thoughts.


Thank you.


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post #2 of 15 (permalink) Old 05-03-2020, 11:04 PM
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Tank size really doesn't matter. It will just determine how long it lasts.


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post #3 of 15 (permalink) Old 05-04-2020, 12:19 AM
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Assuming you have the storage space for it it you'll be fine. Unless you have it already I might opt for a smaller one though, this one would be overkill. It'll last you forever, like a decade. I got a sodastream cylinder (~1 pound) for a 24g tank, I've only been running it for 2 months and so far they've lasted 1 month. Rough extrapolation suggests the 10lb container could last you ~100 months!

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post #4 of 15 (permalink) Old 05-04-2020, 12:36 AM
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Originally Posted by Hujeta View Post
Assuming you have the storage space for it it you'll be fine. Unless you have it already I might opt for a smaller one though, this one would be overkill. It'll last you forever, like a decade. I got a sodastream cylinder (~1 pound) for a 24g tank, I've only been running it for 2 months and so far they've lasted 1 month. Rough extrapolation suggests the 10lb container could last you ~100 months!


A 24 G doesn’t take 10X as much CO2 as 2.5G. A lot of the CO2 is based on surface area and agitation.

I think you’ll get a lot of time out of the cylinder and should do it. I’d do a 20if ya could! It’s not like CO2 is going to expire and you won’t be posting “where do I get CO2?” In a pandemic the next time one comes around!


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post #5 of 15 (permalink) Old 05-04-2020, 03:53 AM
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One pound (454 grams) of carbon dioxide gas occupies 0.2426 m3 or 242,600 cc
10# = 2,426,000 cc..........
From another calc:
https://www.plantedtank.net/forums/9...o2-system.html

6.4 sccm(cc/m, 0 psig, 70F) co2 flowrate in one hour will increase co2 concentration from 0 to 20 ppm in 10 gallon of water.

384 cc/hour..

assuming 10hr/day 3840cc/day =631.7 days!!!! FOR a 10gal tank.

assuming 100% goes into solution

point is for a 2.5gal tank you got a but load of days out of a 10# even w/ low efficiency
though that could lower your days quite a bit.
Can only make a guess at, at worst, 1/2yr...

5# tank and using a small reactor to dissolve the CO2 is probably a better use of space..and funds.

LIST of various users/tanks/gallons for a comparison.
https://www.plantedtank.net/forums/8...tank-last.html

tanks and sizes (rough dimensions)
https://beveragelements.com/product-...co2-cylinders/

YMMV...

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post #6 of 15 (permalink) Old 05-04-2020, 06:04 AM
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@jeffkrol, 6.4sccm is only for the first hour, if keep pumping co2 at 6.4 sccm after the first hour in the 10 gallon tank, the fish are probably floating up side down very soon, lol.

jeff's point is 10lb co2 tank will last a very long time for a 2.5 gallon tank.


to be exact, if co2 injection is 10 hours a day , first hour at (6.4 X 10G/2.5G =) 1.6 sccm co2 flow rate will increase the co2 concentration above 20 ppm, the total volume of co2 in first hours is 1.6 X 60 = 90CC, then the next 9 hours co2 flow rate will keep at 1/4 of 1.6sccm(assume this is the co2 lost rate), to replenish the lost of co2 so the concentration will stay above 20ppm but lower than 30ppm.

1.6sccm X 1/4 X 60minutes X 9hours = 216 cc
90cc + 216cc = 306cc

the total volume of co2 required for the 2.5 gallon tank in a day is 306cc.

10lb co2 tank has about 2430 liter of co2, then 2430liter X 1000(CC/liter) / 306(CC/day) = 7941 day...
about 20 years.


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post #7 of 15 (permalink) Old 05-04-2020, 07:50 AM
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Quote:
Originally Posted by Doc7 View Post
A 24 G doesn’t take 10X as much CO2 as 2.5G. A lot of the CO2 is based on surface area and agitation.

I think you’ll get a lot of time out of the cylinder and should do it. I’d do a 20if ya could! It’s not like CO2 is going to expire and you won’t be posting “where do I get CO2?” In a pandemic the next time one comes around!
To saturate 24g of water compared to saturating 2.5g (both to say 25 ppm) takes 10x as much CO2, how could it not? Of course such a comparison is under the assumption that all other things are equal such as surface agetation and form factor.

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post #8 of 15 (permalink) Old 05-04-2020, 11:22 AM
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That will last a long time! I run a 5# on a 7.9GAL tank and I only refill once a year. CO2 runs for 8hrs a day. With a 10# on a 2.5, it will be literally fill and forget.

As with the other suggestions, even a 5# will last a long time but will take up less space.

Gary


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post #9 of 15 (permalink) Old 05-04-2020, 11:49 AM
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10lb CO2 vs 2.5G tank?

Quote:
Originally Posted by Hujeta View Post
To saturate 24g of water compared to saturating 2.5g (both to say 25 ppm) takes 10x as much CO2, how could it not? Of course such a comparison is under the assumption that all other things are equal such as surface agetation and form factor.


Yes , it takes ten times as much CO2 to saturate the water to same PPM. But over the course of an 8 hour photo period your CO2 usage is not dependent on saturating to same PPM (indeed , we all have the same goal of same Ppm before or shortly after lights on) but how much CO2 it takes to maintain that ppm.



If you have a 2 gallon bucket that leaks half a gallon per hour it takes 6 gallons to fill and keep it full for 8 hours. If I have a 20 gallon bucket that leaks 1.5 gallons per hour it takes 32 gallons to fill and keep it full for 8 hours. So the tank being 10 times bigger doesn’t mean 10 times as much CO2 to get to and maintain ppm. In the made up bucket example for a 10X bigger bucket with 3X bigger “leak off” it was barely more than 5X.


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post #10 of 15 (permalink) Old 05-04-2020, 04:21 PM
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Quote:
Originally Posted by Doc7 View Post
Yes , it takes ten times as much CO2 to saturate the water to same PPM. But over the course of an 8 hour photo period your CO2 usage is not dependent on saturating to same PPM (indeed , we all have the same goal of same Ppm before or shortly after lights on) but how much CO2 it takes to maintain that ppm.



If you have a 2 gallon bucket that leaks half a gallon per hour it takes 6 gallons to fill and keep it full for 8 hours. If I have a 20 gallon bucket that leaks 1.5 gallons per hour it takes 32 gallons to fill and keep it full for 8 hours. So the tank being 10 times bigger doesn’t mean 10 times as much CO2 to get to and maintain ppm. In the made up bucket example for a 10X bigger bucket with 3X bigger “leak off” it was barely more than 5X.
My original rough estimate was based on the assumption that all other factors except water volume would be constant. In your bucket example you don't keep the other factors constant, you increase big bucket volume by 10x and the leak by 3x giving a completely different value of course.

For the small bucket the leak is 25% of the total volume (which I assume should represent the off-gassing of CO2). Using same off-gassing value for the larger tank (represented by a leak), as we assume that tank would have the same form factor/ proportions/ agitation/ biomass etc the large bucket would instead leak 5 gallons per hour. That would add up to leakage of 60 gallons per 8 hours operation meaning it is effectively 10x the leak of the small bucket.

I do realize of course that there's no way OP and my tank share all those factors, but it's the only way to make an estimation of how long the CO2 container would last as if we step away from those assumptions, there's too many unknowns to calculate, if no one else has kept a similar tank with similar conditions of course. Maybe OP intends to keep the water boiling, in a tank with the proportions of an Ikea flatpack? We cannot know that and therefore it would just be a guessing game. I see in the thread several calculations suggesting several years of service anyway.

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post #11 of 15 (permalink) Old 05-04-2020, 05:06 PM Thread Starter
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I'm always in awe with this community, you guys are really awesome. Since it's SUCH a small tank, I don't have space to actually add something to "blow the bubbles" around, I have a HOB, what is the best case scenario for that?


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post #12 of 15 (permalink) Old 05-04-2020, 06:17 PM
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I'm always in awe with this community, you guys are really awesome. Since it's SUCH a small tank, I don't have space to actually add something to "blow the bubbles" around, I have a HOB, what is the best case scenario for that?
I would use a diffuser and just have it placed near the filter return, so that the current can help push the mist around.

Anthony


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post #13 of 15 (permalink) Old 05-04-2020, 06:54 PM Thread Starter
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I would use a diffuser and just have it placed near the filter return, so that the current can help push the mist around.
Good idea, I will try that, thank you!


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post #14 of 15 (permalink) Old 05-04-2020, 07:46 PM
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it sounds like you just need to get a bigger aquarium so you can use up that CO2 faster!

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post #15 of 15 (permalink) Old 05-04-2020, 10:18 PM Thread Starter
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it sounds like you just need to get a bigger aquarium so you can use up that CO2 faster!
I have bigger ones, I just want to carpet this nano tank. :]
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