[APD] pH, KH, CO2 - Now I'm confused

["Scott Reed" <sareedco at comcast_net>]

I am new to this list, and new to CO2 systems, but not that new to
aquatic plants.  I have tried several times to have a nice planted
aquarium, but have always ended up with a fine crop of green hair algae
after a few months.  Now I have purchased a CO2 system, which I am just
starting up today.  Here are the vital statistics:
 
Tank: Oceanic 125 gal (72x18x22)
Lighting:  320 Watts VHO fluorescent on IceCap 660 ballast, URI Aquasun
bulbs
Plants:  Red Rubin Sword, "Kleiner Bar" Sword, "Compacta" Amazon Sword,
Anacharis, Crypt Balansae, Crypt Willisi, Hairgrass
pH:  7.4 (Aquarium Pharmaceuticals Test, before addition of CO2)
KH: 9 (Tetra Test, before addition of CO2)
Temp: 77
Fish:  Various Rainbows, Clown Loaches, Siamensis
New CO2 system:  Dave Gomberg system with needle valve, just started
today, set to 2 bubbles/sec right now
 
My confusion comes from this:  With my pH and KH values, and the charts
given here: 
http://www.thekrib.com/Plants/CO2/kh-ph-co2-chart.html
 
My CO2 level before adding additional CO2 should be between 10 and 15
ppm or between 9 and 12 mg/l (it's hard to tell what the units are for
the first chart, but the text refers to ppm, so that is my assumption)
taking into account the resolution of the tests and the charts. (It
could even be higher, if the pH is really closer to 7.2 than 7.4) This
is at the low end of the optimal range, but still in it, yet the only
thing I grew really successfully was algae.  I tried to test the CO2
level with a Red Sea CO2 test, but got no color change after 25 drops
and gave up, since I knew the CO2 could not be 50! (The test kit was
old, so that may be the problem)
 
My question is this, am I going to see a difference in plant growth with
the addition of CO2 even though I was within the optimal range without
it?  Will the addition of CO2 inhibit the algae growth?
 
I realize I should probably wait and see what happens with the plants,
but I was surprised to see that things should have been ok without
additional CO2.  My confusion comes from the fact that things were not
ok, based on the fine hair algae crop.
 
Thanks for the help!
Scott Reed
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