I think you will find that plants do need some of the minerals removed and you may need to add some back. For my use, I find I can find plenty of plants to grow in hard alkaline water. In St. Clair, I would expect your water to be quite a bit like what I had in the West edge of St. Louis. I'm not a big fan of RO as it seems to be one extra layer or work and I fully admit that is something I try to avoid in my hobbies! When you remove the buffering, you may find the PH difficult to hold steady.