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Re: Alkalinity and Phosphates
James Purchase asked:
> Would a Tannin/Lignin test be of any help in signalling
> when such levels might cause the Alkalinity test to be "off"?
Probably not. Tannins and Lignins aren't likely to be a big
part of the problem. Odd you should mention it though. At
this fall's AGA convention I told Greg Morin and Doug Hill
from Seachem that I thought their next test kit project
should be for total organics. Doug thought that would be
tough to pull off. I agree.
Possibly the most consistent indicator of a problem can
be had by using a direct CO2 test. If the CO2 determined
by the KH-pH method is significantly higher than the results
of a direct CO2 test then there may be some extra form of
alkalinity in the water.
I don't know that the CO2 test kits are any better than the
KH-pH method. The direct tests for CO2 are actually "acidity"
tests. The test depends on the assumption that the measurable
acidity is caused by CO2. By contrast, the KH-pH method
assumes that the measurable alkalinity is all caused by
bicarbonate. The assumptions are very symmetric. Both
methods are subject to the same kinds of interferences, though
from different sources.
That said, my conversations with a people who have used both
methods suggest that in practice the CO2 test kits may be
more dependable than the KH-pH method in planted aquariums.
Another way to tell if you have something other than bicarb
contributing to the KH is to perform an electrometric
titration. That method is potentially very definitive, but
it requires a bit more work and judgement. Anyone who is
interested in electrometric titration can probably find a
more complete description in the archives.