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How long does your CO2 tank last?

puopg

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Hey all, just a curious question for everyone who uses CO2 and is achieving a minimum 1 point pH drop.

For those of you who have larger tanks (like a 120p), about how long does a 10lb CO2 tank last you?
 
I’m into my 5th month now with a 15lb bottle, based on previous experience with a 5lb lasting 2months +, I expect 6 months + with this setup. I have a 40 breeder with a 20 gallon sump.
 
Well, I dont have a 120 gallon tank, but I have 2, 29 gallon tanks and a 20 high that were all being fed by a 5 pound tank and I was having to swap out every 6 weeks at $38.00 per exchange.

I traded in the 5 pound tank and upgraded to a 20 pound when I discovered the 20 pound tank only cost $48.00 to exchange. $200.00 to purchase a 20 pound verses 100.00 for the 5 pound tank. Should be good for close to 6 months…

They gave me full credit on the exchange from 5 to 20 pound tank.

Apparently the gas itself is pretty cheap and the cost to service both tanks is very close. You are paying largely for the labor to handle and fill the tanks and hydrostatically test them and service the valve…
 
I’m jealous, not sure why I blow through tanks so fast. I guess the open nature of an AIO off gassing so much.
@GreggZ has a closed top, so that some CO2 will accumulate above the water and this greatly reduces CO2 losses. This could be a problem for CO2 to stabilise, but this is mitigated by using a pH controller. Net result is CO2 savings plus stability.
 
@GreggZ has a closed top, so that some CO2 will accumulate above the water and this greatly reduces CO2 losses. This could be a problem for CO2 to stabilise, but this is mitigated by using a pH controller. Net result is CO2 savings plus stability.
Ah yeah, I’m wide open and the back chamber is like a river flowing. Add that to my surface agitation.
 
Ah yeah, I’m wide open and the back chamber is like a river flowing. Add that to my surface agitation.

A couple of years ago I have been doing numerical simulations on CO2 in my tank. Computer modelling what happens with CO2 in my tank, based on some basic physics assumptions and measured pH data. These exercises are useful, at best because we could build a scientific experiment to measure the CO2 uptake by our plants and correlate that with the parameters that drive plant health and metabolism, but at least to get a better feel for the balance of CO2 in our tank. It is also therefore that I compared CO2 in an open tank in another thread ( An alternative approach to CO2? ) to heating our home in winter with all windows open. Not only do we totally unnecessarily throw away 90-95% of our CO2 through the "open window", but also will it be harder to have the whole tank nicely stable without fluctuations.

Of course my posts are no longer there, I have no backup, but I remember some nice contributions from other members with an interest in the science of our tank. Perhaps somebody wants to take on this subject again, as we could build a more fact based understanding of our tank that may inspire new ideas.

Now for the question "how long does your CO2 tank last" it is relatively easy to estimate that when we know the tank's surface area (incl sump) as well as the CO2 ppm, under the assumption we have a reactor with 100% efficiency. Remember that a 0.3 pH decrease will correspond to 100% in CO2 ppm and thus around 100% in outgassing (which is the major driver of consumption). Similarly a twice as large tank surface area will give a 100% increase in CO2 consumption. Plants do little, just perhaps 10% of consumption. Surface agitation, as long as it is not very low (diffusion limited boundary layers) and the surface is clean of organic films (use skimmer, overflow, good agitation, airpump), also does little. So to make all the inputs comparable, we should take this into account.
This all is under the assumption of an open tank, where tank water interfaces to ambient air. For (partially) closed systems the above simple assumptions will not apply, and these systems may have a significant reduction (up to 90% or so) in CO2 consumption.
 
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I'm going to start browsing new tank :LOL:
I have a 40 breeder with a 20 gallon sump but I’m looking to upgrade to an AIO in the future just because of the ease of it with maintenance. I love having a sump but I hate doing maintenance down there. It’s mostly because my stand is not designed for it so that’s the biggest issue. But I think that’s the benefit of our setups, we don’t need surface agitation in the display to contribute o2 to the system, the overflow does that for us.
 
that’s the benefit of our setups, we don’t need surface agitation in the display to contribute o2 to the system
I've been thinking about this for a few hours now, and I think you are right. I'm going to reduce the surface agitation to as low as I can next tank change and see what happens.
 
I'm going to reduce the surface agitation to as low as I can next tank change and see what happens.
What benefit would you hope for?

You're experienced, but this seems not good advice for beginners. Besides that, you still need good flow in the tank to distribute nutrients and CO2, as well as to facilitate nutrients uptake at the plant's leaves.
 
I think your missing the point here. Reducing surface agitation doesn’t necessarily mean reducing flow. In my case, I can drop my return lower so as to not cause so much surface rippling. The sump area will by design cause more gas exchange and not require so much surface movement in the display.
 
I think your missing the point here. Reducing surface agitation doesn’t necessarily mean reducing flow. In my case, I can drop my return lower so as to not cause so much surface rippling. The sump area will by design cause more gas exchange and not require so much surface movement in the display.
I agree, but I can't think of any benefit of doing so, while I do see some potential risks. I am trying to understand what we are hoping to gain by doing so?
 
I agree, but I can't think of any benefit of doing so, while I do see some potential risks. I am trying to understand what we are hoping to gain by doing so?
I think the possibility of saving some gas between exchanges. But I think as a whole, the result would likely be negligible, especially with an open topped aquarium. My solution was to just get a larger tank myself, but with a bigger setup your kind of limited to the 20lb tanks unless you get one of those commercial beverage sized containers. Good luck hiding that SOB 😂
 
But I think as a whole, the result would likely be negligible, especially with an open topped aquarium.
I think the value for this thread and other readers is to highlight that it is a misunderstanding that gas exchange is a function of surface agitation. Gas exchange will go down if the surface water gets nearly stagnant, or obstructed by some layer (organics) that hinders gas exchange. Otherwise the gas exchange will just be a function of surface area and partial pressures of the various gasses in water and air, but not dependent of flows. So in summary, I can't think of any benefit in reducing surface agitation nor does it really matter when there is at least some flow and the water surface is perfectly clean.
 
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