Some of what I have read about GH and KH leads me to believe that they are not important parameters and some would have me thinking that you can't grow plants if you are outside of certain ranges. What is the truth? What is the optimal range of each? My tank runs 10 degrees/180ppm GH and 6 degrees/110 ppm KH, could this be causing me problems? Thanks...

Both your GH and KH sound good to me. You would have to be way higher on either to be too much.

That is what I had in my magic water in Marin(well, some 1.2 ppm of PO4 as well). I bred discus and was able to grow and keep anything.

I'm not sure about the range for KH, I guess it depends more on your goals really.
For Tangy's I'd want about 10-12KH, GH about 20. For Altums, a KH of 0-1, GH about 2-3.

Average fish/plants, maybe a KH of 3-4, GH of 4-8.
GH is not very important as long as you have some, Ca/Mg are plant nutrients......

KH is not and thus not particularly dependent for plant growth.
Although some plants will use KH as a carbon source, but they still have some, perhaps limited CO2, so even without it, they can grow, just not as fast if you have low CO2.

Regards,
Tom Barr