Citric acid /baking soda ratio - CO2 Reactor

[Dantel]

Here is the Carbon Dioxide Reactor Kit for those that not sure what it is:


Results: 1:1 ratio is fine or 1.145 Citric A:1 Baking S.(229g citric acid / 200g baking soda)
However, a 1.31 baking soda: 1 citric acid mass ratio is safer, but more on this later

For around 200g/200g powder, ~300g water is okay (it is just a medium where the reaction takes place)

Note: do not exceed the recommended amounts for your bottle, or it might explode if you put a lot more of any of them, even water (takes space). For my bottle, 200g citric acid /200g baking soda /300g water is recommended.


Reasoning (lots of chemistry):
Before I begin, please correct me if I am wrong...

After some research, I came to the conclusion that a 3:1 mol ratio is not quite right.

​

It might look tempting to say citric acid gives 3 protons (H+) to bicarbonate:

H3Cit + 3 HCO3⁻ → Cit³⁻ + 3 H2CO3 → Cit³⁻ + 3 CO2 + 3 H2O

OR
H3C6H5O7 + 3NaHCO3 → Na3C6H5O7 + 3CO2 + 3H2O
Citric acid + 2 Sodium bicarbonate → Disodium hydrogen citrate + 2 Carbon dioxide + 2 Water​

But this reaction looks more like this:

H3Cit + HCO3⁻ → H2Cit⁻ + H2CO3
H2Cit⁻ + HCO3⁻ → HCit²⁻ + H2CO3
HCit²⁻ + HCO3⁻ ⇌ Cit³⁻ + H2CO3
​

So, there are 3 steps to this equation, and in each step, one proton is being donated.



Looking at this table, GPT provided me (I am lazy), we can see the pka values for each step. The first and second protons are being donated quite easily, but the 3rd one has some struggles.

HCit²⁻ + HCO3⁻ ⇌ Cit³⁻ + H2CO3​

For this reaction to move forward, the pKa of the donor acid < pKa of the conjugate acid of the base (That means: the proton goes from the stronger acid (lower pKa) to the weaker acid (higher pKa). The acid is HCit²⁻, and conjugate acid is H2CO3 (carbonic acid)

The carbonic acid has a pKa of 6.37, which is lower than 6.4 for the 3rd proton and therefore not favoured to react. The values are very close to each other, which means some reaction might occur, but it will be at a very slow rate.

Considering the high pressure inside the bottle after 1st and 2nd proton donated, the reaction will shift to the reactant side (or favoured). This is another reason that the 3rd proton is not favoured.

One thing that can be done to force the 3rd proton to be donated is to have a basic solution. This will shift the reaction to the product side as it is more favoured to release a proton.

OTHER IMPORTANT FACTOR
This is to protect your steel bottle. I don't know what brand you are using, but mine is a Chinese, cheap one. Which means they probably used a low-quality stainless steel. If the solution is acidic, it will ruin the bottle over time.

It is better for the bottle to have a slightly basic solution than a slightly acidic one. One reason to use more bicarbonate.


In conclusion:
A slightly more basic solution is more efficient and better for the bottle's longevity.

Why 1:1 mass ratio?

Calculate moles for 100 g each:

moles_citric_acid = 100 / 192.12 ≈ 0.521 mol
moles_baking_soda = 100 / 84.01 ≈ 1.19 mol

Molar ratio (baking_soda : citric_acid):
1.19 / 0.521 ≈ 2.28:1​

I talked about how the 3rd proton won't react most likely. A 3:1 mol ratio is not a very good representation of what's going on

So, if we use a 2:1 mol ratio, then the excess is baking soda (2.28:1), making the solution more basic. A more basic solution will both save the bottle and make the 3rd proton more favourable to be donated.

229g citric acid / 200g baking soda
It looks riskier to me. The 2:1 mol ratio will make the solution neutral in theory, not making it slightly basic to help the last proton be donated. And more likely slightly acidic if the last proton is donated over time.

My questions:
While I spent like +2 hours getting to the bottom of this, I am still not sure about one thing:

• Does 3 baking soda :1 citric acid mol ratio make a more basic solution that will force the 3rd proton to be donated more? If perhaps most of the 3rd proton is going to be donated over time (since we have +a month using the bottle's solution), then do we need the 3:1 mol ratio to be able to use all of the last proton? Or is it just a waste of material and space in the bottle?

One thing is for sure: a 3:1 mol ratio is safer, perhaps.

The nerds, please let me know if there is a mistake somewhere.

Thank you.

 

[Fishfur]

Interesting, but equations make my brain try to run away & hide.

 

[Dantel]

Interesting, but equations make my brain try to run away & hide.

Don't worry, you are not alone (I spent around 3 hours to get comfortable). I think they also look scarier on this website since it is not a good visual representation

 

[Dantel]

Results:

CO2 was active from May 29, 2025, to October 25, 2025 — about five months.

Pressure readings were as follows:

• After 1 hour: 120 psi
• After 19 hours: 220 psi
• After 48 hours: 300 psi
• After 5 months: 20–40 psi

The pressure stayed around 300 psi for about three months. This shows that the reaction was limited by pressure. As the pressure slowly dropped, the chemical equilibrium shifted to the right, causing more of the forward reaction and more CO2 production.

Because my aquarium is small (11.5 L), it took longer for the pressure to fall.

The final solution is clear, yellowish, and quite thick. Slow bubble formation was observed, likely caused by the pressure drop to around 20–40 psi. This again pushed the reaction forward, producing additional CO2.

The pH measured about 6, though this result may not be reliable because I used an API freshwater test kit, which isn’t made for testing the pH of aqueous sodium citrate (Na3C6H5O7).


The bottle shows no rust and appears to be in good condition.


To make a proper final conclusion, I need a more accurate way to measure pH. However, based on the results, the 3:1 molar ratio appears to be correct. Since the reaction continues over a long period, the third proton is eventually donated.

 

[_Fried_Bettas_]

Why anyone would go through this when they could just buy CO2 escapes me. This is far superior to yeast/sugar, but it doesn't have the cost savings to argue in favor of it.

 

[DaveKS]

Why anyone would go through this when they could just buy CO2 escapes me. This is far superior to yeast/sugar, but it doesn't have the cost savings to argue in favor of it.

CO2 bells/ladders are proper way to use yeast driven systems.

Won’t reach saturation levels of diffuser driven systems but totally capable of enhancing med tech type of setup.

 

[_Fried_Bettas_]

CO2 bells/ladders are proper way to use yeast driven systems.

Won’t reach saturation levels of diffuser driven systems but totally capable of enhancing med tech type of setup.

CO2 Reactors work well with yeast as they don't require pressure and are super efficient, as the CO2 is completely dissolved. After trying different options, I will only use pressurized CO2 now and in the future.

 

[Dantel]

Why anyone would go through this when they could just buy CO2 escapes me. This is far superior to yeast/sugar, but it doesn't have the cost savings to argue in favor of it.

A 200g 200g mix would work for anyone. I am just a guy who likes to overcomplicate stuff for himself. This CO2 generator cost me about $100, and with $20 of material, I can run it for years. So, it is much much much more cheaper than any other CO2 system

CO2 bells/ladders are proper way to use yeast driven systems.

Won’t reach saturation levels of diffuser driven systems but totally capable of enhancing med tech type of setup.

Yeah, yeast stuff is too much work. I tried those before. This setup is just put some stuff in and let it run for months. The documentation I did is not clear at all; I will comment a proper documentation here later, but there is no issue. It's just me trying to experiment and find out the best ratio

 

[_Fried_Bettas_]

A 200g 200g mix would work for anyone. I am just a guy who likes to overcomplicate stuff for himself. This CO2 generator cost me about $100, and with $20 of material, I can run it for years. So, it is much much much more cheaper than any other CO2 system


Yeah, yeast stuff is too much work. I tried those before. This setup is just put some stuff in and let it run for months. The documentation I did is not clear at all; I will comment a proper documentation here later, but there is no issue. It's just me trying to experiment and find out the best ratio

I would not call 25% cheaper, much, much, much, and I am willing to pay the extra for simplicity and the ability to essentially set and forget for many months at a time. Actually, there are lower-quality pressurized systems that are about the same price or lower than what you linked. I do understand the attraction of cost-cutting; each person finds what works best for them.

 

[Dantel]

I would not call 25% cheaper, much, much, much, and I am willing to pay the extra for simplicity and the ability to essentially set and forget for many months at a time. Actually, there are lower-quality pressurized systems that are about the same price or lower than what you linked. I do understand the attraction of cost-cutting; each person finds what works best for them.

My bad, I was not fully paying attention to the word I used. I meant much easier. But it is much cheaper than the pressurized CO2 systems. Also, I had yeast systems before, but they were just disasters. They don't last much, and refilling them is a huge pain. In the end, I had to pay consistently to refill them, but this thing lasts for months