An alternative approach to CO2?

[Koan]

You can see the airtight hood:

Wow

Do you have the ability to incorporate an oxygen sensor as well, for livestock?

 

[PeerUnk]

Wow

Do you have the ability to incorporate an oxygen sensor as well, for livestock?

Good thinking yeah, I have the ability and already used two of them in prior projects. But they both been broken (one on my own fault as I dropped it on the floor, the other one stopped reporting valid values after 6 weeks) and the module cost around 60-90 euros. So I won't go there anytime soon. The reasoning is:

Assume the hood is 100% airtight. Air exists of 78% Nitrogen, 21% oxygen and 0.043% (430ppm) and the rest is primarily Argon. When you would add CO2 up to the debatable 15-30 ppm in water (I would go for 10% but hey...), you would need to increase CO2 in the hood by 1-2% (10k-20k ppm). So it doesn't push out any relevant volume of oxygen from the hood (2% times 21%, so oxygen would reduce to 20.5% ). Increasing CO₂ from 430 ppm to 10,000–20,000 ppm only reduces the initial oxygen fraction slightly, assuming the added CO₂ displaces an equivalent volume of air. That displacement alone is not a meaningful oxygen risk.

During photosynthesis CO2 gets converted to oxygen, hence the pearling and increased oxygen saturation. At night it's different, and plants are oxygen consumers and CO2 producers. My tank has an (in-hood) air pump 24/7 to increase diffusion. So any oxygen available in the hood gets transported into the water, trying to get oxygen to 100% (8.3 ppm) and CO2 to 15-30ppm. The volume of CO2 might likely increase greater than the 1-2%. At this point the ventilation disc is opened and fresh air gets into the hood. CO2 volume will be forced down to 10k - 20k ppm. However, I realize that aeration can only transfer oxygen that's actually available in the hood.

So if we are adding relatively low amount of CO2 compared to oxygen in the hood, how can the volume of oxygen in the water drop below a critical threshold? If diffusion rate is low, it makes no sense to monitor oxygen in the water as oxygen in air can be good, but be low in the water. On the other hand If diffusion is good, why should I worry about oxygen, as the system would have enough oxygen to begin with.

The only situation where oxygen monitoring would make sense, when the entire system looses oxygen and no fresh air/oxygen intake would take place. But it does, the hood isn't 100% airtight and gets fresh air at night. Or another situation: when the CO2 sensor fails to measure the correct value, and CO2 is much higher. But then measuring oxygen is no an issue anymore, livestock would be gassed by CO2 already.

So by this reasoning I won't purchase an oxygen sensor soon, but I'll test the tank with just plants and small invertabrates. If all is well after a few months, some fish can be introduced. If the tank crashes or stays unhealthy, I always can get an oxygen sensor to eliminate it as possible cause. Or even better, shut down possible CO2 input and fully open the ventilation disc, so it is a regular CO2 injected tank. And aerating the tank by an external air pump is always possible.

But I agree, all reasoning can be eliminated by an oxygen sensor to begin with, but I didn't have any luck as it broke down.

Cheers!

 

[PeerUnk]

Thank you again, and I believe you pioneer what could emerge as a new CO2 technology over time. It will take time, as we see with the horizontal reactor, but there is no way of stopping concepts that have undeniable benefits. It may take 3-5 years, but you're the first to prove the concept.

I think the solution is still technology dependant and that's okay even interesting from a personal point of view. But in the end the best systems are less dependant on technology. "Keep It Simple". I assume experience hobbyist in high tech tanking know why. I think the horizontal reactor is a good example of keeping it simple. I believe the concept of this alternative approach can deliver stable CO2 as well, and reduce the amount of CO2 used as CO2 can't escape easily by the airtight hood.

We will see in the future how the concept turns out.

If you go for bottled CO2, then I guess the proof of concept would be to inject a steady 0.5 or 1% CO2 in the headspace, stabilise that and run your tank for a couple of months.

I'll buy myself a 500 gr bottle and a new regulator as my old dual stage Vulkan F10/2 need a revision which would get expensive. But yes, It would need to run several months and report back what the results are.