The water in FL comes from an aquifer that sits in limestone, are water here is very hard and its the same water that the fish farms would probably be using. No I doubt it mimics or is the same as the waters in Africa but our water is hard. I never really had to worry about keeping Africans. I don't know the name of the chart he is going by but his range should be 12-18 and its between 2-5 according to his other thread.
To be honest I don't worry about gh/kh but again I also have hard water. I think adding in limestone or holy rock and setting it up would be ok it seems to me that most people just do this. I dont know if it helps or not though. Adding baking soda can help raise the hardness 1 teaspoon/5 gallon. However if you do this you need to make sure you pH is not fluctuating because this can cause a lot of stress on the fish so sometimes its not worth messing with it to much. You would have to do this every-time you change the water and test the levels as its not good to have it fluctuating in a tank full of fish. i would advise testing this out in a bucket or tank with no fish first to see how it affects your water before doing it on your main tank. Also keep in mind that the higher your pH you need to be more aware of your ammonia levels b/c it becomes more toxic in higher pH (of course ammonia should be 0 always but just throwing it out there)