DIY CO2 question. - The Planted Tank Forum
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Old 03-02-2014, 04:27 PM Thread Starter
Planted Tank Obsessed

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DIY CO2 question.

Hello,
My question is:
I want to setup a DIY CO2 system for my 2g. I was wonder if it would make any difference if the bottle the CO2 is crated in is smaller or larger than 2L. Also what sized bottle/bottles should I use for a 2g tank?

Thanks for looking or replying!

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FISHY
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Old 07-06-2014, 03:10 PM
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What did you end up deciding? I have a 3.5 gallon I'm looking to do DIY CO2 in. To my understanding the bottle size is not directly related to tank size, only the amount of yeast used. The bigger the bottle the longer it will last.

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Old 07-07-2014, 04:47 PM
Are these real?

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I would disagree. In my experience, the amount of yeast has very little to do with output, since it will propagate/multiply until some balance is found. The volume of solution is what determines the output. Longevity is determined by sugar concentration, within reasonable ranges. Once all the sugar is converted (or lethal alc levels have been reached) CO2 production stops.

In other words...
• Whether you add 1/8 or 1/2 of a tsp of yeast doesn't matter much. More yeast - quicker startup perhaps.
• A 2l solution will provide about twice the CO2 output of a 1l solution.
• Adding 1/2 cup of sugar will about half the longevity compared to a 1 cup solution.

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Old 07-08-2014, 04:04 AM
Algae Grower

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That is interesting. Thank you for straightening that out. I was just about to put a 1 gallon jug on a 3.5 gallon tank :-/

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Old 07-08-2014, 11:35 AM
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bigger bottle= more water=slower alcohol poisoning of yeast=longer output
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Old 07-08-2014, 05:28 PM
Are these real?

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Quote:
Originally Posted by dzega View Post
bigger bottle= more water=slower alcohol poisoning of yeast=longer output
Only if you change the concentration of the solution. More water / less sugar.

Say we have two bottles, a 2l bottle and a 4l/1gal jug. Let's compare 3 cases:

A) 2l bottle + 1 cup sugar = x days of CO2 production
B) 4l bottle + 2 cups of sugar = ?
C) 4l bottle + 1 cup sugar = ?

The reason why the yeast stops producing can be either the sugar being totally converted into alcohol, or the alcohol concentration gets too high.

So if you compare case A and B, you start out with the same concentration, and assuming the yeast will multiply over a day or two to a given density, B will output twice the CO2, and you will get to the end of production roughly at the same time. With case C, the sugar may run out before the alcohol level gets too high. But I think at the peak of production, you will still have similar CO2 output for B & C.

Think of it that way - using two separate 2l bottles with a given sugar concentration will give you twice the output, but the same longevity as one 2l bottle. If you combine the contents of these two bottles into one, really you still have exactly the same situation.

Besides this, there are a lot of other factors at play. Temperature being one of them - if you can control that, you can somewhat control the yeast output, although then you got other variables like exact yeast strain etc.

Of course, I could be totally wrong.

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