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Re: [APD] KH goes UP after adding CO2

> Date: Sat, 04 Feb 2006 14:10:56 -0600
> From: Barry Anderberg
> Please help!
> Over the past week I have observed a strange thing.. when I add CO2 my
> water's KH goes UP.
> Out of the tap it's 20 dKH. A day after I start injecting CO2 it's up to
> 24. Today (after about 5 days of injecting CO2) it's up to 29...

>> Date: Sat, 4 Feb 2006 13:19:47 -0800
>> From: Liz Wilhite
>> CO2.  CO2 when added to water produces carbonate and bicarbonate.
>> What did your pH do when you added the CO2?
>> CO2 and water form a complex solution with species that occur at
>> different ratios at different pH...

The ratios of each subsequent species is several orders of magnitude smaller 
than the preceeding, so you'd end up with far less bicarbonates than 
carbonic acid and, in turn, far, far fewer carbonates. If you're upping the 
carbonates by 5 degrees Kh, that's roughly 85-90 ppm carbonates working down 
to about 60- gazillion ppm CO2. I don't believe the water will hold that 
much CO2.


>>  If you have a solution that is saturated with carbonate and you add
>> an acid to it you can see it fizz as CO2 is produced.
>> This is the same kind of reaction that occurs when you pour an acid
>> on limestone.

...as the water takes on more CO2 and becomes more acidic, it makes it 
_very_ easy to *dissolve carbonates into solution*. _That's_ the primary 
mechanism that ends up making natural waters so hard.

Barry, are you quite sure that the sand in your tank is silicate? Have you 
tested _it_ with acid? If the amount of CO2 you're adding drives up the 
carbonate hardness that much in such a short amount of time, then even a 
weak acid like acetic (vinegar) should react with whatever is dissolving 
into the water column...


David A. Youngker
jaafaman at comcast_net

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