DIY Pressurised CO2

[matt85]

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!).


To further lower this 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.


Thanks

 

[regani]

What's wrong with just using your standard yeast reactor setup? Much easier and you don't need to repeatedly inject stuff. You can limit co2 flow with a valve if you are concerned you will get too much (unlikely, though).

For any pressurised setup, stay away from glass bottles, you don't want to be around when they explode. Plastic soda bottles are much safer as they are designed to take internal pressure and they don't explode into shrapnel.

 

[matt85]

The thing with the yeast set up is that it's not controlled. I like being in control and yes that thought had crossed my mind, but as the reaction will be controlled the pressure should never get too high, but I will probably pay it safe and use plastic (although sparkling wine would be stored under pressure anyway so those bottles should be able to take the pressure).

 

[regani]

I see where you are coming from. The best control of course is with a proper co2 setup with a regulator and a ph controller but that is a bit pricey.
The only problem I see with your approach is that you generate a lot of pressure to start with which you then hope to retain and release over time. You'll need a good valve to be be able to do that and a bubble counter to monitor it. As the pressure drops in your reservoir the flow of the co2 will drop with it, though. To even out the flow you will probably have frequently adjust the valve. The (physically) weakest point of the system you are proposing is probably the injection site as the seal will be weak there and you may loose pressure.
While your method is good to control the total amount of co2, adding it evenly over time is the tricky bit here, I think.
With a yeast reactor you have less control over the amount of co2 added, but after the initial startup time it will produce co2 with a fairly constant rate for a couple of weeks (depending on the size of your setup). So in a way it is controlled as well.
Anyways, your calculations seem correct so have a go and see how it works out.

 

[dw1305]

Hi all,
I'm not a CO2 user, but if you have a look on the UKAPS forum there is information about what you need for a CO2 system to reliably deliver levels of CO2 (and plant nutrients) that will enhance plant growth.

If you want a yeast based system my suggestion would be the "jelly method" <http://www.aquaticplantcentral.com/forumapc/diy-aquarium-projects/73942-diy-co2-made-easy.html>

Can I ask why do you want to add CO2? If it is just to grow plants you don't need it, you just need to keep away from plants that aren't really aquatic and have a high CO2 demand.

If you choose plants listed in the Tropica "Easy" range they will nearly all grow without CO2 addition. As well as the classic Anubias, ferns and mosses, all floaters (with access to aerial CO2), most Cryptocoryne, Aponogeton and Echinodorus spp., will all grow fine low tech.

If it is to lower the pH of the water? It does, but in a slightly strange manner by altering the CO2 ~ HCO3 equilibrium, and this is different from having naturally soft, acidic water.

cheers Darrel

 

[matt85]

Hi Darrell

I don't know if you remember but you helped me around a year ago and sent me some Amazon frogbit when I was battling high nitrates in my tap water. I have since been able to breed my agassizii, although the fry could only last a few weeks before they were picked off by my other tank inhabitants. Still, a success and I am looking for the next thing to tinker with.

Coming back to the need to inject CO2, I am looking to rid my self of the floating plants as I have found for them to keep nitrates at zero they have to completely cover the surface of the water. This means that not a lot of light gets to the other plants I have and they do not thrive. I also cannot see the fish I have from the other side of the living room! So my next project was to remove the floating plants (perhaps not entirely to begin with) and inject CO2 to see if the submerged plants can step up and take on the nitrate removal. They will also then start to grow better as they will have more light and CO2 won't be limiting their growth.

 

[dw1305]

Hi all,

I don't know if you remember but you helped me around a year ago and sent me some Amazon frogbit when I was battling high nitrates in my tap water. I have since been able to breed my agassizii, although the fry could only last a few weeks before they were picked off by my other tank inhabitants. Still, a success and I am looking for the next thing to tinker with.

Matt I do remember sending the Frogbit. I'm a great Frogbit fan.

Coming back to the need to inject CO2, I am looking to rid my self of the floating plants as I have found for them to keep nitrates at zero they have to completely cover the surface of the water.

I wouldn't remove the floaters all together, I thin down to about 1/2 coverage in the winter and let it got to 3/4 in the summer when there is more ambient light. Usually that means a thin every few days in the summer and every 10 days or so in the winter. When you thin the plants you export the NO3. The great thing about floating plant is that they aren't CO2 limited and show a negative feedback loop where increased nutrients lead to increased growth and greater nutrient removal.

If you thin your floaters you should find that your submerged plants will pick up. I've got a couple of spare Anubias and some Java/Bolbitis fern if they are any good to you?

This Anubias:

You can't really rely on your test kit readings to tell you how much NO3 you have. It would be a lot easier if you could, but some anions are tricky to measure even with lab. scale equipment. That was why I developed the "Duckweed Index", as proxy for nutrient content.

Personally the risk of gassing the fish is always going to outweigh the advantages in plant growth, and even the "safe" limit of 30 ppm dissolved CO2 is only 1/10 of the atmospheric level.

cheers Darrel