DIY Pressurised CO2 - The Planted Tank Forum
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post #1 of 5 (permalink) Old 01-09-2015, 06:52 PM Thread Starter
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DIY Pressurised CO2

Hello all

I was wondering if you could sanity check my idea. All constructive criticism is welcome, as this is just an idea on paper at the moment. I am looking for a controlled way of delivering CO2 to my aquarium, to minimise the risk of over dosing CO2.

I am planning to make a DIY CO2 contraption for providing CO2 to my 75 litre. The contraption will have a reaction vessel (consisting of a 1 litre plastic pop bottle or glass wine bottle- I am yet to decide) containing 500mL of malted vinegar (5% w/v acetic acid). The reaction vessel will be linked to a second vessel and a syringe containing sodium bicarbonate solution. The second vessel will contain water and act as a gas separator and will be further linked to the aquarium water via a diffuser. I will attach valves between each of the components so each can be isolated if needs be. The plan is that the syringe can be used to supply a dose of sodium bicarbonate to the acetic acid which will react and produce CO2. The CO2 will bubble through the gas separator and then into the aquarium, with flow being controlled by the valves. As only a small amount of sodium bicarbonate will be supplied in each dose, there will be no chance of over dosing the CO2 and pressure will remain within manageable limits (and there will be no explosions!).
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post #2 of 5 (permalink) Old 01-10-2015, 12:15 AM
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That is an interesting idea.

Are you going to automate the application of sodium bicarbonate from the syringe somehow?

How would you keep the reaction going evenly throughout the photoperiod? Especially considering you want to avoid excess pressure and the subsequent mess :P.
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post #3 of 5 (permalink) Old 01-10-2015, 06:00 AM Thread Starter
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At the moment it will be a manual injection as and when needed, unless you have any ideas of how it could be cheaply achieved?

And I am hoping that by careful control of the valves the flow rate can be controlled so that it is slow and does not escape all at once. This is something that will require experimentation before I connect to the aquarium however.

To further lower that risk, the concentrations and proportions of the two reactants has been calculated. The target CO2 concentration in the aquarium water is 20ppm or 20mg/L. For a 75 litre aquarium this means that 1500mg (1.5g) is required. As the molecular weight of CO2 is 44.01g/mol, 0.034moles of CO2 is required. The balanced reaction tells us that one mole of sodium bicarbonate and one mole of acetic acid produce a mole of CO2, hence the dose of sodium bicarbonate must be equal to 0.034moles (around 17ml of a 2 molar solution, produced by dissolving 168g in 1litre of water, as it's molecular weight is 84g/mol). Malted vinegar contains 5% w/v acetic acid so the 500ml in the reaction vessel contains just over 0.4 moles (5% w/v gives 25g in 500ml, whilst acetic acid has a molecular weight of 60.05g/mole). This means that there can be over ten doses of sodium bicarbonate before the acetic acid will be depleted and CO2 production will cease.

I am obviously assuming that all carbon dioxide will be diffused successfully and that each dose will last a reasonable amount of time (a few days would mean a month could be achieved before the vinegar would need replacing).

I hope that anyone with experience of using CO2 could point out any major oversights and/or changes needed before I attempt to make this.

The supply of bicarbonate will be manual I unless you can think of a cheap way of automating it? And I am hoping that by control of the valves that the supply can be made to last a decent amount of time sui that it doesn't ask ever the aquarium all at once, but this will require experimentation when one I have made it.

Last edited by Darkblade48; 01-12-2015 at 06:40 AM. Reason: Please use the edit function for back to back posts to keep threads cleaner
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post #4 of 5 (permalink) Old 01-11-2015, 05:11 AM
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a very similar idea that I have heard is to have a large container full of the baking soda (no need for an aqueous solution) and set up a drip of vinegar into it. I think that you will find putting the vinegar into the baking soda rather than the other way around will simplify things quite a bit

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as always, any comments, questions or criticisms are greatly appreciated.
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post #5 of 5 (permalink) Old 01-11-2015, 05:20 AM Thread Starter
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Why is that so? If you calculate the amount of each that is needed, as the vinegar only contains 5% w/v acetic acid would it bit be best for this to be in excess?
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