# How long will a 2.5 lbs bottle of CO2 last?



## snowhillbilly (Mar 29, 2006)

I have a 55g standard tank. It has about 12 plants in it right now. It is only under an 80 watt light. How long would a 2.5 lbs tank of co2 run for. I sthis tank to small would i be filling it all the time. I plane on putting alot more plants in and i figure i should get a better lighting system just dont know how much is to much. lol


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## hooha (Apr 21, 2005)

It's probably easier/more affordable getting a 5lb tank. If you're going to go high light, you will probably use more C02 eventually as well. A 5lb tank on my 55 lasts about 4-6 months. I got a 2.5lb tank for a 20 gallon and if I remember correctly it's cost was close to a 5lb tank (got it for space concerns).


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## kwc1974 (Jan 4, 2006)

the longevity of a CO2 bottle is dependent on your KH value
I have a 55G and my KH is thru the roof 21KH, and I have to stream in the CO2 to get a proper level, my 5lbs tank will last 4-6 weeks
My friend has a 75G and a KH of 8, his 5lbs bottle will last him 4-6 months. BIG differance in time & money


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## DubSack (Mar 20, 2006)

KWC, I think your mistaken. Just because you have a high KH, it doesnt mean that you have to pump in more co2 to reach the same ppm. Youll have the same co2 levels if you KH is 2 or 10. The only thing that changes is your PH.

A 5 Lb tank will last the same amount of time wether you KH is 2 or 12.


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## Sully (Nov 11, 2005)

Yes if you can get a larger cylinder 5-10 lb. Largest you can get.

But my 2.5 lb is going strong at 3 months on a 30 gallon tank.

-SULLY


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## John P. (Nov 24, 2004)

My 2.5 lb bottle lasted 15 months or so, with 30ppm CO2 in the water, on my 26G. CO2 bubbled into my Eheim 2213.


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## banderbe (Nov 17, 2005)

I agree w/ you, high KH shouldn't mean more Co2 required.

My KH was 18 when I was on tap water. Now I use 100% RO reconstituted with a KH of 3, and I use the same amount of CO2.

However, the author Hans Baensch who publishes the awesome tome known as the Aquarium Atlas says that indeed more CO2 is required for a higher KH, so I don't know what to believe other than my own experience.



DubSack said:


> KWC, I think your mistaken. Just because you have a high KH, it doesnt mean that you have to pump in more co2 to reach the same ppm. Youll have the same co2 levels if you KH is 2 or 10. The only thing that changes is your PH.
> 
> A 5 Lb tank will last the same amount of time wether you KH is 2 or 12.


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## Bert H (Mar 2, 2004)

> I agree w/ you, high KH shouldn't mean more Co2 required.


 Not sure about that. I have a kh of 9-10, and I learned if I don't run my CO2 24/7 I can't get my pH low enough during the photoperiod.

Unless I am mistaken, a higher kh = more buffering ability. More buffering ability = more difficulty in changing your pH, which would possibly require more CO2 to change that pH.

Any chemists care to comment?


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## DubSack (Mar 20, 2006)

thats sort-of along the lines I was thinking Bert. It is much harder to lower your PH when you KH is at 9, but I dont think that any less co2 is being absorbed in the water. It just harder to lower the PH. Also, the ph/kh chart for measuring co2 isnt perfictly accurate, especialy if your dealing with really high KH levels. It's more of a guidline than anything else. The higher your KH, the more inacurate the chart becomes. Not to mention that the test kits people use are deffanitly not 100% accurate.


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