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Re: Aquatic Plants Digest V1 #188
>I don't suppose anyone has an opinion of Kent Marine pH Stable?
>
>The label states the contents as Carbonic Acid Monosodium Salts.
>Strangely enough, it is supposed to increase buffering capacity.
This makes no sense to me unless their definition of buffering capacity is
different from mine. I take buffering capacity to be synonimous with
alkalinity, in which case this statement is wrong. Carbonic acid is in
equilibrium with CO2, so adding carbonic acid salts is chemically
equivalent to CO2 injection. Adding CO2 changes pH without changing
alkalinity or acidity (see Spotte, Sea Water Aquariums 1979). CO2 does
however change carbonate hardness, which may be what they mean by buffering
capacity. This is a dumb definition of buffering capactity though, since if
you increase H3O+ ions along with an increase in the carbonate &
bicarbonate ions you have no NET change in the waters ability to resist
downward changes in pH, which is what any reasonable working definition of
sea water buffering capacity should require.
>Stranger yet, I can never get the increase to show up with a test kit.
Not surprising.
>I haven't put any in the tank since I can't get it to work in my test
>cases. It also states that it may take up to 24 hrs for the change,
>but I didn't read any change in that amount of time.
Maybe they think that since the cabonic acid increases bicarbonate, the
bicarbonate would be left behind even after the CO2 (and hence acid) is
driven off by aeration, thus resulting in a net gain in alkalinity after 24
hours of aeration. This seems very dubious to me, but you would need a
chemist to comment on it I'm afraid.
> Perhaps there
>is something else in the "equation" that is not in RO water?
>
Doubt it...RO water is supposed to be pure, making the equations a lot
easier to figure out than tap water.
>The problem is that by the time I get RO water buffering capacity
>up to ~80 ppm using baking soda, the pH is ~7.5.
>
Aerate the water, since it is likely to be supersaturated with CO2
immediately after adding baking soda. Once the excess CO2 is gone the pH
will reach its equilibrium value of 8.2.
internet email: Grant.Gussie at phys_utas.edu.au
www page: http://reber.phys.utas.edu.au/~gussie/