KH/pH/CO2 and Non-Carbonate Buffer Systems

I'm wondering if somone can enlighten me on the concept of KH/pH/CO2 and
the use of non-carbonate buffers.  I understand that KH can be
influenced by non-carbonate buffers (such as phosphate buffers).  The
reason I am asking this is because of the natural pH of my water as well
as the KH builder that I'm using.  My tap water has a pH of 7.8.  Now, I
use RO/DI filtered water so I need to regenerate it with something.
I've tried both a mix of RO with tap water, and RO with Kent products.
Kent's KH builder (called pH Stable) is a carbonate based buffer and has
a natural pH of 7.8 same as my tap water.
I keep Discus in my plant tank and I like to keep my pH at around 6.6.
I don't like having to drop my pH so far and would like to lower my pH.
However, adding an acid to the water just depletes the KH rather than
drop the pH.  Kent's pH Minus is simply sulfuric acid.  After I add it,
the pH does drop a bit but over the course of an hour will rise back to
7.8.  I've tested this is a 10g tank filled with KH=5 water.  I added
enough pH Minus to drop the pH to 4.0.  By next morning, the pH was back
to 7.8.  The KH had dropped to 2.  After adding more, I managed to get
the pH to drop but at the expense of having no KH.
SeaChem makes an Acid buffer that is a Zwitterionic buffer.  They say it
is not so much a pH Minus product but a product to buffer your water at
a certain pH.  All I know is that it is a non-phosphate buffer.
I'm wanting to drop the tanks natural pH to 7.0 so that with CO2
injection I only have to drop it a few tenths of a point (to 6.6) rather
than 1.2 points.  This became a problem the other day when I changed CO2
cylinders.  I must have screwed up the needle valve setting when I moved
the regulator to the other tank.  The bubble rate was too slow to keep
up with CO2 loss and the solenoid heated up, causing the entire assembly
to become warm.  This caused the needle valve to expand and completely
shut off CO2 flow.  Overnight the pH went from 6.6 to 7.8.  I was
suprised not to find a bunch of sick fish.  Amazingly the Discus and
their tankmates looked perfectly happy.  I'm now in the process of
dropping the pH back down but I'm holding at 6.9 until I get some
I guess I need to separate the solenoid from the needle-valve so that
the temperature doesn't vary so much.  I could also switch to a 12V
solenoid and use a transformer.
Would the addition of SeaChem's product screw up anything?  I suspect it
would make my KH read artificially high.  Would I really care if all of
my buffering capacity was made up of SeaChem's buffer as opposed to a
carbonate buffer?  Would my Lamotte CO2 test kit still be accurate?
Would I still target the 5 degree KH mark as I always have?  From what I
understand, alkalinity/KH test kts don't test specificly for carbonate
buffers, is this correct?  My Lamotte alkalinity test says it is testing
ppm CaCO3 and that does confuse me.
Sorry for the babbling.  Maybe I'm being too obsessive about this, but I
do like knowing exactly what is in my water and being able to control
it and I'm restricted from using pure tap water.  The water is clean,
but is very hard (300ppm) and has a very high alkalinity (240ppm).
Mike from St. Louis
vandi at well_com