Does peat humic acid affect CO2 measurement

[Stephen Pushak <teban at powersonic_bc.ca>]

Carlos Munoz <cmunoz at crystal_cirrus.com> wrote:
> Water filtered by peat contains pH buffers other than carbonates, so the
> standard pH/KH/CO2 tables will *not* work.  The same buffers will interfere
> with direct CO2 tests, so forget about a C02 kit also. 

I know I have always been saying this but Roger Miller said he wasn't so
sure. He thought that there would have to be a very high concentration
of humic acid in the water in order for the contribution to alkalinity
to be significant to affect the CO2 test kit titration because the
organic molecules are very large. I don't have the figures he quoted at
hand, maybe he does. 

It does occur to me that we could have fairly significant concentrations
of humic acid in the water. After all, there is enough to make a
significant yellowing of the water. Back in the days of the blue water,
yellow water debate, somebody might recall what the concentration of
humic acid might be when you begin to get a noticeable yellowing of the
water. My water was very yellow in the peat tank for a month or more and
even now I'm sure the yellow color is quite noticeable. You can easily
see yellow in the water when its in a white bucket. Previously, you
could see the yellow when you looked at the tank. BTW, I think it would
be ok to use even less peat than I did if you just want a little organic
matter to help the iron reduction process in the substrate.

> Your best bet is to make an estimate based on your bubble rate and look
> at your plants to see how they're doing.  Even just a little extra CO2 
> helps a lot.  Make sure you have good circulation _below_ the water surface 
> and that the water surface itself isn't disturbed too much.

Another way to deduce the CO2 concentration is to estimate your
carbonate hardness (from tap water analysis and by guessing how much you
add) and then observing the pH change in a water sample when the CO2 is
driven off overnight or by boiling. It's not really a good estimate
because I think carbonate molecules get used up in some biological
processes so the carbonate hardness will be less than what you calculate
it to be from additions.

Does this make sense Roger? At least we could put an upper and lower
bound on the CO2 concentration by this method.

Steve P
Join the Aquatic Gardeners Association, eh

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