CO2 and pH changes

> From: Thomas Price <tprice at u_washington.edu>
> I have been adding a little bit of baking soda to correct this, and am
> able to reduce this change to about 0.2 points.  I don't mind doing
> this, but want to be sure that it's not dangerous to my aquarium in
> non-pH ways.
> The tank is 20gal, lighting is one 24" GE plant and aquarium and one
> Phillips Daylight fl. bulb.  I have five 3" angelfish, two corys, a
> clown loach, and three otocinclus.  Because of the angels, I don't
> want to use a remedy which increases the hardness, if possible.

As far as I know, KH is not a factor when setting the hardness of the
water for specific fish. General Hardness (GH, calcium and magnesium
hardness) is the type that affects the biological well being of the
animals and plants. 

We have moderate KH (3-5 dKH, 50-90 ppm) in our angel and discus tanks
and all residents are doing fine.  We keep the GH low in these tanks
(1-2 dGH).