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KH Drop

Thanks for the response.. Just a few questions,
If adding CO2 lowers your KH, then those tables
showing the relationship between pH-KH-CO2 don't
really make a whole lot of sense. I was under the 
impression that the KH remains stable and pH drops as
you add CO2.  Is that not right?? Also, if I leave the
water out of the tank to let the CO2 escape, isn't the
damage already done as far as reducing the alkalinity
of this particular water? Without adding more calcium
buffers, the KH will still be low regardless of the
amount of CO2 right?

>>Paul Krombholz wrote:
You changed the substrate, added driftwood, and you
started adding 
DIY CO2.  Of the three changes, I think the CO2
additions would have 
the greatest effect on lowering the KH.  KH is a
measure of 
alkalinity, and the test is done by adding acid until
the pH drops to 
around 4.2.  The test kit solution has a color
indicator dye that 
changes color at around 4.2. The more acid you have to
add, the 
higher the alkalinity.   By adding CO2, you add
carbonic acid, a weak 
acid which lowers the pH, and, of course, also lowers
the alkalinity. 
Try taking a cup or two of your tank water and let it
stand for 24 
hours, which should be long enough for the excess CO2
to escape into 
the atmosphere.  Then check the pH and KH.  Both
readings should be 
higher.  If they are not, then the source of the acid
is either the 
Profile or the driftwood, or both.
Paul Krombholz in well-watered central Mississippi,
thundershowers the last four afternoons.

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