My kH is 0 according to the test kits. Ofcourse its more like less than 1 but higher than 0. I dose ferts after all.
My pH is wicked low though. Like 5.1 sometimes 4.5 in my co2 injected tanks. Having said that, I never really had a problem with kH for plants. It was always more about not having enough of some nutrients for me.