CO2 (&pH?) level at different tank locations

scottward

Guru Class Expert
Oct 26, 2007
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Brisbane, Australia
Hi Tom.

I have been doing a lot of reading about CO2. I now appreciate that this is the area where I should be focussing all (most) of my attention.

I was reading last night about how you used an expensive CO2 probe to check CO2 levels at various places within a tank; interesting stuff - I was under the impression that the CO2 would be reasonably evenly distributed throughout the tank.. but I can see that's not the case.

I'm just wondering - what happens with pH in all these areas?

Assuming the kH remains the same, which it would, if you measure one area near where the CO2 is entering the tank and find 100ppm, and then in another spot you only measure 10ppm - doesn't this mean that the pH will be different in different places of the tank too? Wouldn't this case issues with the fish as they constantly swim through 'patches' of water with differing pH?

I can't see any reason how the pH could not change if the CO2 is 'patchy' ?

Maybe you've already answered this but I've missed a thread somewhere...:)

It seems that circulation is a whole lot more important than I thought too! I read something about putting the plants in the middle of the tank and letting the water swirl all the way around them. This seems like the best way of getting good circulation. It seems very difficult to get good circulation yet good dense planting - any tips on how to best achieve this?

Scott.
 

VaughnH

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Jan 24, 2005
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As I recall, a few months ago Tom reported that the pH doesn't change with the variations in concentration of CO2, or at least doesn't change fast enough to track well with the concentration. I think this is understandable because the pH/KH/CO2 relationship is an equilibrium relationship, which has to take some time for the water to adjust to.

My experiment using a reverse flow undergravel filter to distribute CO2 into the water seems to work, and I suspect that it gives reasonably uniform distribution, if you discount the plants usage of the CO2. But, of course, you can't discount that, so even that method would result in wide variations in CO2 concentration, with the lowest concentrations being right where it is needed the most.

CO2 mist being swirled around everywhere in the tank looks to me like it would stand the best chance of achieving good concentration even in thick stands of plants. But, enjoying the appearance of the water when it is filled with microscopic bubbles takes some adjusting to.
 

scottward

Guru Class Expert
Oct 26, 2007
958
10
18
Brisbane, Australia
VaughnH;37127 said:
As I recall, a few months ago Tom reported that the pH doesn't change with the variations in concentration of CO2, or at least doesn't change fast enough to track well with the concentration. I think this is understandable because the pH/KH/CO2 relationship is an equilibrium relationship, which has to take some time for the water to adjust to.

My experiment using a reverse flow undergravel filter to distribute CO2 into the water seems to work, and I suspect that it gives reasonably uniform distribution, if you discount the plants usage of the CO2. But, of course, you can't discount that, so even that method would result in wide variations in CO2 concentration, with the lowest concentrations being right where it is needed the most.

CO2 mist being swirled around everywhere in the tank looks to me like it would stand the best chance of achieving good concentration even in thick stands of plants. But, enjoying the appearance of the water when it is filled with microscopic bubbles takes some adjusting to.

Ok I see. I thought the water would change pH instantly though.

I remember reading about your reverse flow UG filter idea. Sounds like a good idea and a good concept to experiment with.

Yeah - my tank looks like a glass of lemonate at the moment! As long as the plants grow well I don't mind. ;-)