On Wed, 2 Jul 2003 19:47:34 UTC, "Paul Davies"
wrote:

You make some interesting points. Coincidentally, my tap water is, like
yours only 60-70ppm carbonate. In my 100gallon tank, at 2 bubbles per second
CO2, I have difficulty in getting the pH below 7.0, which equates to
10-12ppm CO2. To get to the 20ppm CO2 which the gurus recommend, I would
need a pH of about 6.75. This would need an awful lot of CO2, and I don't
believe my reactor could dissolve at that rate.

My question is :- are you saying that adding baking soda will give me "free"
CO2? If you could possibly do a little more to convince me, I will certainly
give it a try.

Tom Barr has already given a good answer, I see. To change the
independent variable from the way he put it: Adding bicarbonate will let
you have more dissolved CO2 at your favorite pH level, like 7.0 or
whatever, than you would with your plain tap water.

It's not free, in that you have to keep pumping CO2 in. First you have to
pump extra CO2 to bring the pH back _down_ where you want it after adding
the bicarb. Then, because your level of free CO2 is higher than before --
that's what you wanted, after all -- the stuff will escape more rapidly,
and you'll have to replace it more rapidly.

The too-rapid escape of CO2 because of too much mixing with air would
raise the pH if you allowed it to; but in practice that means you'll have
to add CO2 a little faster to keep the pH steady.

(This is an exercise in saying the same thing several different ways.
It's the only way I can grasp problems that have several variables that
all affect each other.)


--
Dan Drake

http://www.dandrake.com

Outer Planets update: Uranus, Neptune, Pluto, the check
in the mail, the weapons of mass destruction.