CO2 and water temperature - The Planted Tank Forum
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post #1 of 25 (permalink) Old 01-02-2016, 01:54 AM Thread Starter
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CO2 and water temperature

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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post #2 of 25 (permalink) Old 01-02-2016, 02:04 AM
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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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post #3 of 25 (permalink) Old 01-02-2016, 05:17 AM
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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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post #4 of 25 (permalink) Old 01-02-2016, 02:07 PM Thread Starter
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Originally Posted by essabee View Post
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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post #5 of 25 (permalink) Old 01-02-2016, 02:54 PM
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CO2 and temperature

Quote:
Originally Posted by Axelrodi202 View Post
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, 20C (68F) you have 30 ppm CO2.
Under pH 6.7, KH 4, 25C (77F) you have 28 ppm CO2.
Under pH 6.7, KH 4, 30C (86F) you have 26 ppm CO2.
I think the differences are quite small to worry about.
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post #6 of 25 (permalink) Old 01-02-2016, 03:22 PM
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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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post #7 of 25 (permalink) Old 04-04-2017, 03:57 AM
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Quote:
Originally Posted by 58417 View Post
Under pH 6.7, KH 4, 20C (68F) you have 30 ppm CO2.
Under pH 6.7, KH 4, 25C (77F) you have 28 ppm CO2.
Under pH 6.7, KH 4, 30C (86F) 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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post #8 of 25 (permalink) Old 06-27-2017, 10:19 PM
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Red face Best answser

Quote:
Originally Posted by 58417 View Post
Under pH 6.7, KH 4, 20C (68F) you have 30 ppm CO2.
Under pH 6.7, KH 4, 25C (77F) you have 28 ppm CO2.
Under pH 6.7, KH 4, 30C (86F) 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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post #9 of 25 (permalink) Old 06-27-2017, 10:42 PM
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disregarding pH:




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post #10 of 25 (permalink) Old 06-27-2017, 11:36 PM Thread Starter
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What are the Y axis units?

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post #11 of 25 (permalink) Old 06-27-2017, 11:46 PM
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Quote:
Originally Posted by Axelrodi202 View Post
What are the Y axis units?
I was looking more for "relative" changes so it wasn't critical.. but this is a reference:
Quote:
But carbon dioxide is relatively insoluble in water exposed to the atmosphere, being theoretically soluble to the extent of only 0.5 ppm at 20C, and 1.0 ppm at OC 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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Last edited by jeffkrol; 06-27-2017 at 11:56 PM. Reason: edit
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post #12 of 25 (permalink) Old 06-27-2017, 11:58 PM
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Quote:
Originally Posted by jeffkrol View Post
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..
44.01 g/mol for CO2

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

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post #13 of 25 (permalink) Old 06-28-2017, 04:19 AM
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Quote:
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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Last edited by jeffkrol; 06-28-2017 at 04:26 AM. Reason: edit
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post #14 of 25 (permalink) Old 06-28-2017, 04:35 AM
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Quote:
Originally Posted by jeffkrol View Post
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
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.

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post #15 of 25 (permalink) Old 06-28-2017, 04:44 AM
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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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