I don't do African rift cichlids so I will let others comment on that.
I follow Tom Barr's suggestion that he made when he visited GSAS a couple of years ago. I asked him about his recommendation FOR water hardness and he said he targets about 5.0 dGH and doesn't worry about dKH as long as there is no danger of PH crash. We have very soft water here in Seattle. I use Seachem Equilibrium for raising the dGH to Tom's recommendation and if necessary add enough NaHCo3 (baking soda/bicarbonate of soda/sodium bicarbonate) to keep my dKH at about 2.0. My plants seem to do well at these levels and no PH problems.
I use the Seachem calculator
to determine how much Equilibrium to add to raise my dGH and this calculator
to determine how much NaHCO3 to add to raise my dKH.