Re: Why does KH drop?

[Greg Morin <greg at seachem_com>]

>Well, yes, I have driftwood in the tank. But, before putting together the
>tank, I kept the wood for several weeks submerged in a rubbermaid trash can.
>The wood includes swamp rootwood from aquariumdriftwood.com and malaysisan
>driftwood. The wood did leach a small, barely noticeable tanin. I measured
>the water parameters out of curiosity, just to see how and if this type of
>driftwood would change the water chemistry. They were still close to the
>tap water values after all that time, so I'm assuming the driftwood wasn't
>the cause. Since everything else was kep constant, I'm blaming the kH drop
>on the Flourite by lack of a better explanation. Maybe I should try to
>reproduce this effect under more controlled conditions. If I ever find
>time to do that (being very busy lately) I will report back here.

What was the KH in the tap water before and after soaking with the 
driftwood? I think what you're seeing here is an equilibrium effect. 
The acids are leaching out but also being pulled back in to an 
extent. So after some time there remains a fairly constant level of 
acids from the wood in the water column. When you raise the KH you 
shift the equilibrium of the acids such that most of the dissolved 
acid is neutralized, which has the counter effect of causing more 
acids to be leached from the driftwood to make up for this loss, as 
that happen they continue to react with the added KH until an 
equilibrium is once again achieved at fairly low KH level. So no 
matter what you you do to raise the KH in that tank with the 
driftwood you're going to see this effect. A control experiment would 
be to soak the driftwood like you did before in the trash can but add 
buffer to raise the KH and monitor the rate and degree of loss of KH. 
It should be very cose to what you see in the tank (it may be a bit 
slower because there are other organic acids produced in a tank as 
well).

-Greg Morin
-- 

Gregory Morin, Ph.D.  ~~~~~~~Research Director~~~~~~~~~~~~~~
Seachem Laboratories, Inc.      www.seachem.com     888-SEACHEM
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~