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Water chemistry, when heating/raising temp. a few degrees..

MickeM

Active Member
5 Year Member
Messages
441
Location
STOCKHOLM , SWEDEN
Hi everyone..

Recently I visited a website created by a "pool and pond" company.
I their info text about KH.. they mention that KH have a tendency to get lower due to the biological processes increasing when raising the temperature in the water... the carbonates gets "absorbed" in a larger amount
than in a cooler water...
Since I have been nagging about changes in the quality (KH/GH/EC/TDS) of the water in my Apisto breeding tanks when I am cleaning some of the sand and changing some water...(without having tested the water !!)....

I wonder....

Have anyone else in this forum any statistics /experiences concerning this effect ?????

/MickeM
 

dw1305

Well-Known Member
5 Year Member
Messages
2,755
Location
Wiltshire UK
Hi all,
I think dKH may fall with increasing temperature, but I don't think it is very relevant to us.

There are 3 different routes for a fall in carbonate hardness. The first is a biological one, at higher temperatures increased microbial nitrification will deplete carbon (as CO2) and this effects the CO2 ~ HCO3- equilibrium. This is relevant to grossly polluted water, but not really to our fish tanks.

The other 2 factors both relate to the chemistry of the CO2 ~ HCO3- equilibrium, unusually many carbonates (including both calcite and aragonite morphs of CaCO3) are less soluble at higher temperatures, and in common with all gases CO2 is less soluble at higher temperatures as well.

There is a more complete explanation of this at: <http://comp.uark.edu/~ksteele/gochemfiles/SteeleCarbonatePC-762.htm>

cheers Darrel
 

Mike Wise

Moderator
Staff member
5 Year Member
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11,202
Location
Denver, Colorado, U.S.A.
Darrel's right. I learned all about the carbonate cycle in a Sedimentary Petrology class in grad school. Wonderful book, Carbonate Environments, but not applicable to aquariums.
 

gerald

Well-Known Member
5 Year Member
Messages
1,491
Location
Wake Forest NC, USA
... and of course plants are also consuming carbon (CO2, HCO3-) and thus lowering KH.
In the very narrow temp range we keep aquaria, I doubt if the temp effect is noticeable.
But in a pond that goes from freezing (very low biological activity) to 30 C it sure would be.
 

dw1305

Well-Known Member
5 Year Member
Messages
2,755
Location
Wiltshire UK
H all,
"and of course plants are also consuming carbon (CO2, HCO3-) and thus lowering KH." They are, but the difference with plants is that (above light compensation point) they are producing oxygen, which raises pH (but not dKH).

My suspicion is that in soft water for all practical purposes you can ignore the changes in pH and water chemistry that relate to the changes in the CO2 ~ HCO3- equilibrium during photosynthesis.

cheers Darrel
 

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