Note, the gas build up is not N2, nor O2. It is CO2. N2 and O2 are very tough to dissolve.
CO2 gas builds up, not the others.
Why? CO2 dissolves easily right?
Does the CO2 dissolve FASTER when you have aquarium water with say 2 ppm of CO2?
Or say 40 ppm of CO2?
We assume that the CO2 dissolving rate is the SAME. But is this correct?
What types of test can we do, as aquarist, to see and get a good idea?
1. You can add O2 gas and see how long it takes for a chamber full to dissolve, it takes a long time(measure this, say 10 minutes).
But you need O2 gas, but that's available from gas places for torches etc.
2. You can also run a CO2 reactor on a small powerhead loop inside the sump. While doing a water change, the tank water STOPS flowing into the sump water. the sump water is a relatively small volume, but has a high rate of CO2 gas being added, not the entire tank. So the reactor quickly fills up. But wait....I thought CO2 dissolves really fast?
No, not as NEAR as fast when the water is say 1-2 ppm of CO2.
When you start the tank pump back up, the gas bubble disappears in a less than 1 minute(say 45 seconds) with a tiny bubble head at the top. You can add CO2 to the chamber and fill it with pure CO2 and repeat this process. You get the same time for dissolving.
You can also stop the CO2 late in the day when gas bubble forms(since we assume we are not sure what the gas actually is).
Then do a large water change(removed the CO2 gas from the main tank) and the gas bubble quickly dissolves in 45 seconds again.
There are no other gases that dissolve this quickly in the aquarium. If it was a hard to dissolve gas like Ar, N2, O2, the bubble would remain, but it does not.
Try it and see.
I'm trying to think of a problem with this deduction. But I do not know of any other potential gases that would dissolve so rapidly once the level of CO2 and O2 ppm are dropped suddenly.
This means as concentration of CO2 builds up, the ability for the system to dissolve the gas into solution changes. This makes common sense also. It's harder to add something when there's already a bunch of it in there.
The other issue is that as the concentration increases in the tank, the degassing RATE also increases.
Fick's 1st law predicts this.
This is a decent reference for some of what is going on.
However, few models include degassing rates. Which is what we have going on also. A sump has a much small area for degassing and much less water to add gas to.
Tokumura, M., Baba, M., Kawase, Y., Dynamic modeling and simulation of absorption of carbon dioxide into sea water. Chemical Engineering Science, 62, pp. 7305-7311 (2007).
What do these graphs suggest at high CO2 dosign rates?
Now if you increase the volume of water suddenly(say goign from the just thr sump water, to the entire tank and sump volume of water), does the rate remain the same?
No! It does not.
Note, this does not include the degassing rate increase either.
As we add more CO2 into the aquarium over **time***, the reactor has more and more trouble dissolving the CO2 since the concentration of CO2 increases.
So simply testing which gas stays in the gas phase(O2, N2 etc) and which dissolves rapidly, we have our gas of interest................ pretty well identified.
The graph above also looks a lot like this graph:
If this gas was O2, we should see higher O2 ppm than if the gas was CO2 alone.
But I have an O2 meter. The O2 does not change.
My next test is adding a probe holder into the CO2 reactor top. That should pretty much resolve any questions.
I have a pH probe and then an O2 LDO. So I can assume O2 to have minimal pH effect, CO2, rapid. O2, well, if it's all O2, then.......that should be measured as well.
I can get small bottles of N2 and O2 at the CO2 gas supply place also. This has been a nagging question for me for some time. While I'm convinced, I want to be more certain.
CO2 gas builds up, not the others.
Why? CO2 dissolves easily right?
Does the CO2 dissolve FASTER when you have aquarium water with say 2 ppm of CO2?
Or say 40 ppm of CO2?
We assume that the CO2 dissolving rate is the SAME. But is this correct?
What types of test can we do, as aquarist, to see and get a good idea?
1. You can add O2 gas and see how long it takes for a chamber full to dissolve, it takes a long time(measure this, say 10 minutes).
But you need O2 gas, but that's available from gas places for torches etc.
2. You can also run a CO2 reactor on a small powerhead loop inside the sump. While doing a water change, the tank water STOPS flowing into the sump water. the sump water is a relatively small volume, but has a high rate of CO2 gas being added, not the entire tank. So the reactor quickly fills up. But wait....I thought CO2 dissolves really fast?
No, not as NEAR as fast when the water is say 1-2 ppm of CO2.
When you start the tank pump back up, the gas bubble disappears in a less than 1 minute(say 45 seconds) with a tiny bubble head at the top. You can add CO2 to the chamber and fill it with pure CO2 and repeat this process. You get the same time for dissolving.
You can also stop the CO2 late in the day when gas bubble forms(since we assume we are not sure what the gas actually is).
Then do a large water change(removed the CO2 gas from the main tank) and the gas bubble quickly dissolves in 45 seconds again.
There are no other gases that dissolve this quickly in the aquarium. If it was a hard to dissolve gas like Ar, N2, O2, the bubble would remain, but it does not.
Try it and see.
I'm trying to think of a problem with this deduction. But I do not know of any other potential gases that would dissolve so rapidly once the level of CO2 and O2 ppm are dropped suddenly.
This means as concentration of CO2 builds up, the ability for the system to dissolve the gas into solution changes. This makes common sense also. It's harder to add something when there's already a bunch of it in there.
The other issue is that as the concentration increases in the tank, the degassing RATE also increases.
Fick's 1st law predicts this.
This is a decent reference for some of what is going on.
However, few models include degassing rates. Which is what we have going on also. A sump has a much small area for degassing and much less water to add gas to.
Tokumura, M., Baba, M., Kawase, Y., Dynamic modeling and simulation of absorption of carbon dioxide into sea water. Chemical Engineering Science, 62, pp. 7305-7311 (2007).
What do these graphs suggest at high CO2 dosign rates?
Now if you increase the volume of water suddenly(say goign from the just thr sump water, to the entire tank and sump volume of water), does the rate remain the same?
No! It does not.
Note, this does not include the degassing rate increase either.
As we add more CO2 into the aquarium over **time***, the reactor has more and more trouble dissolving the CO2 since the concentration of CO2 increases.
So simply testing which gas stays in the gas phase(O2, N2 etc) and which dissolves rapidly, we have our gas of interest................ pretty well identified.
The graph above also looks a lot like this graph:
If this gas was O2, we should see higher O2 ppm than if the gas was CO2 alone.
But I have an O2 meter. The O2 does not change.
My next test is adding a probe holder into the CO2 reactor top. That should pretty much resolve any questions.
I have a pH probe and then an O2 LDO. So I can assume O2 to have minimal pH effect, CO2, rapid. O2, well, if it's all O2, then.......that should be measured as well.
I can get small bottles of N2 and O2 at the CO2 gas supply place also. This has been a nagging question for me for some time. While I'm convinced, I want to be more certain.
