# CO2 and water temperature



## Axelrodi202 (Jul 29, 2008)

Gases are more soluble at lower water temperatures, with oxygen being the most commonly cited example of this in planted tank circles. However CO2 should follow this rule as well. If lowering an aquarium's water temperature (by a substantial amount, say 5 degrees Fahrenheit) - what should be done to the CO2 injection rate? Should it be decreased because the CO2 will be more soluble in water, or should it be kept the same because increased dissolved O2 will balance it out?


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## Maryland Guppy (Dec 6, 2014)

5 degrees is not much.
You will have test by de-gassing samples.
Trusted hobby method is 30ppm for every 1.0 change in pH.


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## essabee (Oct 7, 2006)

Keep the temperature best suited to the fauna you have in the tank and don't worry about the solubility of gasses being affected by temperature. The changes in solubility hardly matter for the purpose you use CO2.


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## Axelrodi202 (Jul 29, 2008)

essabee said:


> Keep the temperature best suited to the fauna you have in the tank


This is what I'm looking to do; I started driving my canister filter w/ a new external pump and the heat from the pump has led to a tank temperature a few degrees higher than optimal for my inhabitants, so I am adjusting the heater to compensate and lower the temperature back down. Hopefully I won't have to tinker with my CO2 flowrate as a result.


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## 58417 (Dec 18, 2012)

*CO2 and temperature*



Axelrodi202 said:


> If lowering an aquarium's water temperature (by a substantial amount, say 5 degrees Fahrenheit) - what should be done to the CO2 injection rate? Should it be decreased because the CO2 will be more soluble in water, or should it be kept the same because increased dissolved O2 will balance it out?


Under pH 6.7, KH 4, 20°C (68°F) you have 30 ppm CO2.
Under pH 6.7, KH 4, 25°C (77°F) you have 28 ppm CO2.
Under pH 6.7, KH 4, 30°C (86°F) you have 26 ppm CO2.
I think the differences are quite small to worry about.


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## mistergreen (Dec 9, 2006)

Heat excites the gases causing them to bounce out of the water. They bounce out less frequently in colder temps.
Let you fish be the guide.


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## rstampa (Jan 29, 2017)

58417 said:


> Under pH 6.7, KH 4, 20°C (68°F) you have 30 ppm CO2.
> Under pH 6.7, KH 4, 25°C (77°F) you have 28 ppm CO2.
> Under pH 6.7, KH 4, 30°C (86°F) you have 26 ppm CO2.
> I think the differences are quite small to worry about.


What if the temperature in my 65 gal planted aquarium is 85 degrees but my ph is 7.6 and my KH is 4? I am running a 5lb CO2 tank and diffusing it through my 350 gph power-head 6bps.


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## rstampa (Jan 29, 2017)

*Best answser*



58417 said:


> Under pH 6.7, KH 4, 20°C (68°F) you have 30 ppm CO2.
> Under pH 6.7, KH 4, 25°C (77°F) you have 28 ppm CO2.
> Under pH 6.7, KH 4, 30°C (86°F) you have 26 ppm CO2.
> I think the differences are quite small to worry about.



This is the best answer I've read so far. Thanks, you've been a big help,


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## jeffkrol (Jun 5, 2013)

disregarding pH:


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## Axelrodi202 (Jul 29, 2008)

What are the Y axis units?


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## jeffkrol (Jun 5, 2013)

Axelrodi202 said:


> What are the Y axis units?


I was looking more for "relative" changes so it wasn't critical.. but this is a reference:


> But carbon dioxide is relatively insoluble in water exposed to the atmosphere, being theoretically soluble to the extent of only 0.5 ppm at 20°C, and 1.0 ppm at O°C as shown on Fig. 57.


10 to the -3rd power Moles/Liter is fairly easy..
44.01 g/mol for CO2 

.44ppm I believe but for some reason math isn't working out in my head..


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## Dman911 (Nov 24, 2016)

jeffkrol said:


> I was looking more for "relative" changes so it wasn't critical.. but this is a reference:
> 
> 
> 10 to the -3rd power Moles/Liter is fairly easy..
> ...


That chart shows carbon monoxide which is much less soluble than carbon dioxide from what I have found.

Nevermind its the chart above...duh! but what's the conversion of the chart above? the same?

Dan


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## jeffkrol (Jun 5, 2013)

> Solubility, X_1, of CO2 in water.
> Handbook of Chemistry & Physics,
> 34th ed., 1953, Solubility of Gases
> in Water, p. 1532. The curve is the
> best–fit, fifth order by the author.


Above is where the odd charts from
X_1 is just a symbol or notation apparently
Molar solubility.. Don't ask me.. 
How to Calculate Solubilities | Sciencing
Best I can guess is grams CO2/100G of water..
Seems an archaic term to me..
Like this only multiplied by 10 (kg of water)









If you can see the teenie tiny numbers on the right (0-1ppm CO2)
Can't believe I can't find a decent chart..








20C 68F .5ppm (sat), 30C 86F .4ppm (sat)


As to the CO I could pretend it was just to show O2 but actually it was just an oppsie..
28.01g/mole CO
.02801g/L


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## Dman911 (Nov 24, 2016)

jeffkrol said:


> Above is where the odd charts from
> X_1 is just a symbol or notation apparently
> Molar solubility.. Don't ask me..
> How to Calculate Solubilities | Sciencing
> ...


Thanks, the reason I am asking is I read somewhere (I think the krib) that at equilibrium under atmospheric pressure co2 concentration will be 2-3 ppm so that leaves a lot of room for difference in the interpretation of measuring Co2 and was trying figure a way to be more accurate about my specific location, temp etc. If its only 2ppm then at 1.2 PH drop that would be 32 ppm and if it was 3ppm at 1.2 PH drop then it would be 48ppm. A bit of a difference.

Dan


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## osmosis (Apr 19, 2017)

Well the solubility has been covered, but the flux is also important. At higher temps, wont plants metabolize CO2 faster? You will also evaporate CO2 slightly faster. This means any drop in solubility is probably made up for needing to add more to maintain the same concentration.


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## Dman911 (Nov 24, 2016)

osmosis said:


> Well the solubility has been covered, but the flux is also important. At higher temps, wont plants metabolize CO2 faster? You will also evaporate CO2 slightly faster. This means any drop in solubility is probably made up for needing to add more to maintain the same concentration.


 @osmosis I hate you for understanding all this stuff. The chemical reaction side of things in this hobby drive me nuts to no end trying to understand it. I am honestly considering taking some courses to get a minor grasp. 

Dan


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## jeffkrol (Jun 5, 2013)

Atmospheric replacement also comes into play.. 
As CO2 is depleted it will drive more atm CO2 into solution..
Obviously replacement can easily be exceeded by fast depletion..or injection would not be necessary..

Then there is diffusion..

Point is its a dynamic situation w/ multiple parameters and sinks..


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## StevieD (Jun 17, 2017)

I wondered if someone would be so kind as to explain ATM in reference to A Planted Tank. I only know of two. ATM = At the moment or Automated Teller Machine.

Thanks in advance

SD


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## jeffkrol (Jun 5, 2013)

StevieD said:


> I wondered if someone would be so kind as to explain ATM in reference to A Planted Tank. I only know of two. ATM = At the moment or Automated Teller Machine.
> 
> Thanks in advance
> 
> SD


ATM one atmosphere of pressure..at sea level I believe.


> 14.70 pounds per square inch
> 
> Standard sea-level pressure, by definition, equals 760 mm (29.92 inches) of mercury, *14.70 pounds per square inch*, 1,013.25 × 10 3 dynes per square centimetre, 1,013.25 millibars, one standard atmosphere, or 101.325 kilopascals.Apr 19, 2017


just used to define a standard condition.. and to avoid confusion of conditions. Solubility for most things change w/ increasing pressures..
Why beer releases gas when opened..


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## Vohlk (Apr 8, 2016)

osmosis said:


> Well the solubility has been covered, but the flux is also important. At higher temps, wont plants metabolize CO2 faster? You will also evaporate CO2 slightly faster. This means any drop in solubility is probably made up for needing to add more to maintain the same concentration.


Solubilities in these charts are measured as an equilibrium so rate of evaporation is equal to the rate of absorption. If you go from a cold solution to a warmer solution what you say is true that the CO2 evaporation will increase, but otherwise assuming constant temperature and concentration it should not change.
As plants begin to metabolize CO2 at a faster rate the rate of absorption from the atmosphere to water will increase, this is proportional to the difference that the CO2 concentration in solution is from its theoretical equilibrium point(as displayed in these charts).
For example if you can theoretically achieve 26 ppm CO2, but your plants bring that value down to 23 ppm, then the rate of absorption will increase. At this point you get into reaction kinematics to determine if the rate of absorption by the plants is too fast to be matched by the rate of dissolution from the atmosphere. That rate of dissolution increases as the waters ppm of CO2 drops, aka dissolution is faster at 22ppm as opposed to 24 ppm. 
This is proportional but not linearly related meaning at some point the plants absorption will overcome dissolution, when that occurs I do not know and there are a lot of factors that influence this.

Something else to consider is how plants react to lower CO2 concentrations and if as CO2 concentrations drop do plants absorb more or less CO2 as a result, I am not a biologist I definitely do not know this but maybe someone else here does? This will influence the kinematics as well.

Also one thing to note is that KH will affect equilibrium values as well, the graphs given look like good guides to get started with but won't be exact numbers. Higher KH buffers pH drop but allows overall more CO2 absorption, lower KH increase pH drop but should allow for overall less CO2 absorption.


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## Dman911 (Nov 24, 2016)

I'm just gonna sit here and wave to the people out the back window of the short bus. By the way I'm taking the names of you chemists out there for future questions, my gain your loss. 

Dan


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## osmosis (Apr 19, 2017)

Vohlk said:


> As plants begin to metabolize CO2 at a faster rate the rate of absorption from the atmosphere to water will increase, this is proportional to the difference that the CO2 concentration in solution is from its theoretical equilibrium point(as displayed in these charts).


Henry's Law only applies to systems in equilibrium. Our tanks are no in equilibrium with the air in our houses. The low partial pressure of CO2 in your house would lead to very low dissolved CO2 levels, so we inject CO2 to bump up the solution concentration. CO2 absorbing from the air is negligible unless you have a tight lid on your tank that doesn't let the CO2 escape.


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## Vohlk (Apr 8, 2016)

osmosis said:


> Henry's Law only applies to systems in equilibrium. Our tanks are no in equilibrium with the air in our houses. The low partial pressure of CO2 in your house would lead to very low dissolved CO2 levels, so we inject CO2 to bump up the solution concentration. CO2 absorbing from the air is negligible unless you have a tight lid on your tank that doesn't let the CO2 escape.



I see you meant for systems with added CO2, they are at steady state, which is similar to a forced equilibrium, assuming no change in the amount of CO2 you add to your tank (begining of CO2 addition and the end of it) (begining of day/end of day) your tank will achieve a steady state/equilibrium (not the same but for henrys law it requires steady state not necessarily equilibrium (confusing and sometimes used interchangably). It can also be called dynamic equilibrium which is the correct form of equilibrium and satisfies Henry's law requirements.


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## StevieD (Jun 17, 2017)

*Short bus rider x 2*



Dman911 said:


> I'm just gonna sit here and wave to the people out the back window of the short bus. By the way I'm taking the names of you chemists out there for future questions, my gain your loss.
> 
> Dan


Sits next to Dan and waves to them'ns that unnerstands *stuff*. We'll get 'em pal just wait n see!


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## roadmaster (Nov 5, 2009)

Dman911 said:


> I'm just gonna sit here and wave to the people out the back window of the short bus. By the way I'm taking the names of you chemists out there for future questions, my gain your loss.
> 
> Dan


Me too!
Mustn't forget to put our helmet's err,,,thinking caps on.:hihi:


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