why would some plants grow best in soft water? why can I grow all the tough toninas with a kh of less than 1? I know they suffer for lack of co2.. when mine went out they grew poorly and the fluviatiilus is only now recovering.

but don't they melt in a high kh tank?

ah or are you saying, that these are among the plants that would not make it in a kh run tank...

I am comfortable with co2 far more so than adding kh.. but it is what I know.