generally SA cichlids need very soft, acidic water and african cichlids need very hard, alkaline water, so you will not be mixing them in the same tank.
also, while ive never keept africans, I always thought they needed a large tank (min 300L). I could be wrong there may be a way to do a small african tank.
The general idea with pH is that you use a buffering agent like proper pH, i guess for africans proper pH 8.2: http://www.hollywoodfishfarm.co.nz/product_detail.php?id=279
hardness is a bit trickier. I think limestone would be the way to go but Ive not used it.
all the best