JDAVIS at bio_tamu.edu writes:

I have been thinking about this driftwood problem...and could it be that the
tannins from the driftwood have a buffering capacity???

	Tannins are organic acids. (I think that all of them are, but am 
not sure.) The wood contains a lot of tannic acid and humic acid, if I am 
not mistaken. The wood acidifies the water by leaching these acids.