Gh is the hardess of your water...The Kh I am referring to is your waters ability to hold a steady Ph, basically. I have a VERY low Kh which mean without the buffer my Ph wil drop like crazy. You can have hard water that still has little buffering capabilities. That is why I said to check your Kh just to be sure it is high enough as well.
A Gh and Kh of over 200 is good for africans.