I think the waste gas you are referring to is atmospheric (mainly nitrogen) which has very low solubility in water compared to CO2. So in systems where you start up initially with air trapped inside it can take a very long time to purge out. But once you have Co2 it will actually dissolve out into water very quickly.
In this reactor I had about 300 cc of atmospheric air when it was initially turned on. It took about 4-6 hours for it to be completely dissolved in water and eliminated so there is actually no need for a separate purge circuit.
When CO2 is pumped in it dissipates within a few minutes.
To be clear all the gas is completely dissolved in the water there are no microbubbles or mist coming out of the discharge line. The key is circular flow
inside the reactor. This pushes big bubbles to the center where they rise up. Microbubbles are on the side and gradually dissipate at the bottom. here is a schematic:
I plumbed the reactor on a closed recirculating loop (about 400 GPH). The loop is interconnected via a T to a sump and another T to a pump. The pump pulls out CO2 rich water from the recirculating loop at 0.5 GPM and sends it to my tanks.
The maximum CO2 airflow that the reactor can fully dissolve is 0.3 LPM (3-5 bps in contrast is about 0.02 LPM)!!
..so its very heavy gas flow that can be successfully dissolved by this reactor. Obviously I run it at only about 3 bps to support 300 gallons of tankage but you can see that with this design its possible to deliver a massive amount of CO2 (far more than is practically required!).
At 3 bps on the recirculating loop I tested the pH of water extracted by the 0.5 GPM pump that's pumping to my two tanks. dKH = 7,pH before CO2 was turned on = 7.8, after 30 minutes of CO2 at 3 bps pH of water delivered from reactor is 6.2 (this was the limit of my API test kit so pH could be lower).
Therefore the CO2 ppm is 90ppm. I am only delivering it at a slow rate to my tanks so the tank ppm is close to 30 ( by drop checker).
I think if I was to increase the flow from the reactor into my tanks the ppm would be even lower but its not required.
I think to be able to adequately delivery CO2 to approx a 300 gallon volume without the 7Up effect is really worth it.
The next step will be to design a more compact version with lower flow. I think I can do that in a 2' x 24 " cylindrical column. If any one is interested in trying one out please let me know.
Sounds nice in THEORY, but it's not the case practice, particularly after the about 4-8 hours of running.
I have sumps and CO2 systems that run independent of the return pumps, so if I shut the return pump off, then do my water changes, leave the CO2 running, the pH drops to about 5.3 vs say 6.0 normally in the tank.
The level inside the reactors also goes from maybe 1/2 way down, to the bottom of the reactor tube, roughly 12" or 24" depending on the chamber size.
Is this all N2 gas too? No, the CO2 does NOT dissolve in a linear fashion as you add more, the sump is a small volume and the CO2 builds up, and as it does so, so does the FLUX out of the of the water/sump. So more degassing takes place. It's like running uphill in the sand, 2 steps forward(adding more CO2), 1 step back(more faster rates of degassing).
Fick's 1st law of diffusion predicts this.
These are not sealed systems since the inflow and out flow water is exposed to the air rather quickly. There is also lag times involved.
Observations in real aquariums:
So after my water change, what happens to all that CO2 inside the chamber? In about 1 minute it is all gone.
So why would ANY gas build up if it is NOT CO2?
If you do not add ANY CO2 to a reactor, does it magically fill with gas later in the day? Is CO2 gas we buy very impure? No, it's pretty much 99.90% pure or higher, FDA regulations for beverage grade. So that could be a source.......but why does the level inside my chamber fill so rapidly if the N2 is so hard to dissolve into water?
Something does not add up.
But the new water after the water change is poor in CO2, not rich.
Another way to test this:
You can take the sealed hang on CO2 reactor chamber after several hours of operation, use valves to shut both ends and place it on a different say non CO2 enriched tank, the gas will dissolve rapidly and go into solution. N2 gas does not do that. O2 also does not do that either. You can bleed air into the chamber and try this also. There should be a big difference between the time it takes to dissolve the gas from the build up of CO2 over a few hours vs the same volume of air in the same CO2 reactor.
This is an old issue and I think I'll do this myself to check another way to show this vs the sump thing.
Thank you, gave me a new idea to test it.