I'm not a fan of crushed coral in Rift Lake aquariums for the simple reason that so many African species are substrate sifters- which can lead to injury when they begin sifting through a substrate full of sharp pieces of coral and shells. The same thing applies to the coral background. As nice as it may look, there is a huge potential for injury when a fish brushes against a piece of it.
In my experience with African species, sand is the best substrate. Caribsea makes a type called "Sahara Sand" that is specifically made for African cichlids- and it looks great! It's supposed to help maintain a high pH, but since my water is liquid concrete- I couldn't speak on those capabilities. Plus, all those rocks, shells, etc. you add to the tank will also help keep the pH high.