Do you mean what type of rocks are those? Well they are a whole bunch of texas holey rock. Here in Chicago though the rocks are very expensive ($7 per pound) so I have invested a lot of money in those rocks, but they are a type of limestone. Limestone is great in cichlid tanks because it leaks things into the water raising the ph which is needed. They also create tons of caves and because of cichlids distinct personalities, you can find that each of them finds their own caves and acts as though it is their home. Great rocks and perfect for african cichlids. Also in case you are wondering, I am using just plain regular play sand. I was sick of the crushed coral as it irritated my cichlids so I went in my shed and happened to find play sand. I cleaned it off and it works like a charm. You aren't limited to the type of sand really though because you can also use pool filter sand which is normally more white, or you can even go with ocean sands or argonite (maybe i spelled that wrong) as these types of sands also help because they raise the ph as well. Good luck and can't wait to see you tank when it is up and running.
It looks great and IMO the perfect setup for cichlids. Maybe some people don't really maintain their tanks 
Either way, I'm gonna still use it.
