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Re: [APD] KH question

I don't think it's pedantic. I think Vaughn makes a very good point that is often missing from discussions that use the term "buffer." Often folks say that adding a carbonate will buffer the water, apparently meaning that it will tend to resist changes in pH. Whether adding something like CaCO3 will make the aquarium water tend to resist changes in pH depends on what what you put in and else is in the water. For example if you use CaCO3, it will tend to hold the pH well above 8 (around 10 iirc) provided that you use enough that the pH is that high and some of the CaCO3 is precipitated or remains undissolved. The precipitated/undissolved CaCO3 will dissolve if small amounts fo acid are added and hold the pH steady until there is no more precipitate left, then the pH will fall if more acid is added.
I think most often, when folks say "buffer" what they really mean is "alkaline", except for true buffer products such as the Seachem product mentioned. Even with true buffers, you have to have enough of it in the water for it to work.

----- Original Message ----
From: Vaughn Hopkins <hoppycalif at yahoo_com>
To: aquatic plants digest <aquatic-plants at actwin_com>
Sent: Monday, November 20, 2006 12:08:30 AM
Subject: Re: [APD] KH question

Where I live now my tap water has KH below 1.  I don't add anything  
to "buffer" it.  I use 40 ppm of CO2 in the tank, and the pH hasn't  
changed enough to cause either the fish, shrimp or plants to complain.

Incidentally, to buffer a solution requires adding a substance that  
resists increases in pH and a substance that resists decreases in pH  
- always two substances.  Adding just one, like bicarbonates, only  
shifts the pH higher, it does not buffer the solution to a specific pH.

I just felt a need to be pedantic there.  Sorry.


On Nov 19, 2006, at 10:20 AM, Liz Wilhite wrote:

> I moved recently and went from tapwater with a KH of 9 to tapwater  
> with a KH
> of 2.  The KH in the tank with aragonite is about 6, but the Eco- 
> Complete
> tank is running about 3.  I am just getting my CO2 up and running  
> again and
> I have a question:  with a KH of 3 do I run a risk of the pH  
> crashing?  If I
> need to raise the KH, could I expect to see a consistent, stable KH  
> level if
> I added a bit of crushed coral to the canister filter?
> Thanks.
> -- 
> Liz

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