Why are you worried about your KH level? From the tap my KH is 16, GH is 20.
I have 4 planted tanks, mostly rainbowfish and tetras, and lots of types of
plants that are doing very well in those conditions. If I were you I wouldn't
fight your water, just use fish and plants that really don't care about your
KH. In fact you are a bit ahead with higher KH, as you have natural buffers in
your water and you'll be able to maintain a nice constant pH with the CO2.
Folk with softer water have all kinds of problems with massive pH swings with
their CO2 as their water isn't well buffered.