I worked hard for months to keep my first RCS tank at the "recommended" 6-7 GH and the only berried female I ever had turned out to actually have a terminal case of green fungus. Then took my eye off the tank, the rocks must have exhausted the Amazonia soil and one day I discovered the water had popped up to 10 GH and 4 KH. Since then it's been full of babies from the new Goldenback neo's I added, so go figure! (I should add though that I'm convinced my original RCS were all somehow infertile as the remaining 5 still haven't bred to this day).
So I'm becoming skeptical about the importance of hitting some magical KH/GH/pH levels (within reason anyway, and especially for 'easy' neo's etc) and I think that actually what @Zoidburg
and @Blue Reef Ridge
have said about diet and how you go about water changes is probably way more important than abstract water parameters.