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.
