Planted Tank Enthusiast
Join Date: Aug 2006
Location: Cincinnati, Ohio
I believe plants can also use KH, which would cause it to lower. Don't quote me on that though.
13 dKH is on the high side. Do you know your GH? My water was fairly compareable (ie. liquid rock)
Your level of concern should be determined by what you want to grow/raise in your water. There's some plants which people have more success with in soft water, but water hardness shouldn't be a huge problem with plants.
There's also some species of fish/inverts which prefer soft water. For example, I never had very good luck with german blue rams in my hard water, nor have I had any luck with CRS. I invested in an RODI system so I could try out some of the soft water species of shrimp and fish. (CRS, Apistos etc.).