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- #121
This post is to summarise my understanding of the physics in the reactor, how to explain a remaining gas pocket after CO2 has been turned of, but arguably this post is less relevant for most users.
I recently had some PM exchange with a friend who observes an unexplained gas pocket in the reactor, that at least partially remains after the CO2 has been turned off at night. I usually don't observe that in my reactor (but it can sometimes happen) and I believe I now understand what is going on when it happens
The short story is - don't worry, unless too little CO2 is injected and as a consequence the tank and reactor have not yet reached (or will never reach) equilibrium.
Gases in fluids and in gas pockets try to reach an equilibrium of partial pressures (*). This is how CO2 absorbs in water (high partial pressure in pure CO2, lower in water), or how also oxygen and other gases diffuse in and out from the tanks water surface.
Now when we have pure CO2 in our reactor, this gas pocket will initially have zero partial pressure of O2, N2 and other gases than CO2, and therefore the gas pocket 'sucks' these gases from the tank water trying to reach equilibrium of partial pressures with the water. Some time after we stop injecting CO2 in the evening, the relative proportions of gases in the reactor will gradually approach equilibrium with the tank water, and as a consequence the gas bubble will not fully dissolve (different from what you would be expected with a pure CO2 gas pocket).
Now the point is, as I said, don't worry as long as we inject enough CO2 in the reactor. We can look at the three modes of operation of the reactor to make this point
-1- Overflow mode, as I use it. In overflow mode the reactor purges itself, as discribed earlier in the threads on horizontal reactor and CO2 Spray Bar. This purging will continuously push a little gas out from the reactor, and hence keep it perfectly pure CO2. By the end of the day the pure CO will dissolve, and (nearly) no gas will be left in the reactor.
-2- Inject with a precision CO2 regulator / CO2 needle valve. No CO2 can get 'lost', so ultimately all CO2 that comes from the regulator must get absorbed in the water. If there would be too much other gas (non CO2) in the reactor, the reactor CO2 absorption efficiency will go down, then the reactor will purge itself, until it reaches the state that all CO2 flow from the regulator will be absorbed in the water. So also here no problem.
-3- Inject with a pH/CO2 controller. Very similar to to argumentation -2-. No problem, the controller will guarantee that we reach target CO2 and stability, irrespective of the reactor purging itself in the process.
When injecting too low CO2, we are effectively continuously on the search for equilibrium, and our tank water has not yet stabilised nor has our reactor purged itself. So it is a process in transition. The solution is, whatever mode of operation is used, to inject enough CO2 for the tank and CO2 system to reach equilibrium.
(*)
en.wikipedia.org
Note:
Like so many others, I post on this forum and enjoy time talking with fellow hobbyists because I am passionate about the hobby, learn from others and get inspired, but also try to help and give back as much as I can. ScapeCrunch is a place where I have met some remarkable people, and sometimes there is even more good stuff going on in PM’s than on the public forum.
Not all planted tank fora are as open to innovation and new ideas as ScapeCrunch, and regretfully their members won’t have access to all new ideas in the hobby. As an example, we’ve been keeping tanks with bubble reactors for three decades, but after my post with a step-by-step description on how to optimise these reactors was deleted by another forum's admins , some recent ‘advice’ I see posted is inadequate and leading back to where too many reactors make noise, are not stable, are underpowered or spit CO2 mist and bubbles in the tank -- the struggle for two or three decades and continuing today, that could easily be avoided when having a clear 'cookbook recipe' for setting up and optimisation of a vertical bubble reactor.
Our hobby needs an open, constructive, innovative forum like ScapeCrunch, and in my view its creation was some time overdue. Anyone lurking around on this forum as guest to check out on reactors, please join ScapeCrunch and reach out, on the forum or in PM’s, to me and several people who are passionate about making CO2 injection simpler and easier, and share the passion for this hobby in general.
Yugang (CJR)
I recently had some PM exchange with a friend who observes an unexplained gas pocket in the reactor, that at least partially remains after the CO2 has been turned off at night. I usually don't observe that in my reactor (but it can sometimes happen) and I believe I now understand what is going on when it happens
The short story is - don't worry, unless too little CO2 is injected and as a consequence the tank and reactor have not yet reached (or will never reach) equilibrium.
Gases in fluids and in gas pockets try to reach an equilibrium of partial pressures (*). This is how CO2 absorbs in water (high partial pressure in pure CO2, lower in water), or how also oxygen and other gases diffuse in and out from the tanks water surface.
Now when we have pure CO2 in our reactor, this gas pocket will initially have zero partial pressure of O2, N2 and other gases than CO2, and therefore the gas pocket 'sucks' these gases from the tank water trying to reach equilibrium of partial pressures with the water. Some time after we stop injecting CO2 in the evening, the relative proportions of gases in the reactor will gradually approach equilibrium with the tank water, and as a consequence the gas bubble will not fully dissolve (different from what you would be expected with a pure CO2 gas pocket).
Now the point is, as I said, don't worry as long as we inject enough CO2 in the reactor. We can look at the three modes of operation of the reactor to make this point
-1- Overflow mode, as I use it. In overflow mode the reactor purges itself, as discribed earlier in the threads on horizontal reactor and CO2 Spray Bar. This purging will continuously push a little gas out from the reactor, and hence keep it perfectly pure CO2. By the end of the day the pure CO will dissolve, and (nearly) no gas will be left in the reactor.
-2- Inject with a precision CO2 regulator / CO2 needle valve. No CO2 can get 'lost', so ultimately all CO2 that comes from the regulator must get absorbed in the water. If there would be too much other gas (non CO2) in the reactor, the reactor CO2 absorption efficiency will go down, then the reactor will purge itself, until it reaches the state that all CO2 flow from the regulator will be absorbed in the water. So also here no problem.
-3- Inject with a pH/CO2 controller. Very similar to to argumentation -2-. No problem, the controller will guarantee that we reach target CO2 and stability, irrespective of the reactor purging itself in the process.
When injecting too low CO2, we are effectively continuously on the search for equilibrium, and our tank water has not yet stabilised nor has our reactor purged itself. So it is a process in transition. The solution is, whatever mode of operation is used, to inject enough CO2 for the tank and CO2 system to reach equilibrium.
(*)
Henry's law - Wikipedia
Note:
Like so many others, I post on this forum and enjoy time talking with fellow hobbyists because I am passionate about the hobby, learn from others and get inspired, but also try to help and give back as much as I can. ScapeCrunch is a place where I have met some remarkable people, and sometimes there is even more good stuff going on in PM’s than on the public forum.
Not all planted tank fora are as open to innovation and new ideas as ScapeCrunch, and regretfully their members won’t have access to all new ideas in the hobby. As an example, we’ve been keeping tanks with bubble reactors for three decades, but after my post with a step-by-step description on how to optimise these reactors was deleted by another forum's admins , some recent ‘advice’ I see posted is inadequate and leading back to where too many reactors make noise, are not stable, are underpowered or spit CO2 mist and bubbles in the tank -- the struggle for two or three decades and continuing today, that could easily be avoided when having a clear 'cookbook recipe' for setting up and optimisation of a vertical bubble reactor.
Our hobby needs an open, constructive, innovative forum like ScapeCrunch, and in my view its creation was some time overdue. Anyone lurking around on this forum as guest to check out on reactors, please join ScapeCrunch and reach out, on the forum or in PM’s, to me and several people who are passionate about making CO2 injection simpler and easier, and share the passion for this hobby in general.
Yugang (CJR)
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and drop checker starts heading to yellow.. am thinking of maybe staying at 5.5ph next week as 5.4ph mite be to much of a drop for fish..
