Well im going to contradict tazman. Just a little bit. Ok i have over 15 some where in at 17 African cichlids plus fry in my 55 gallon. Its a male an female tank. 1 male 3 females Yellow labs. 1 male 3 female Elongatus. 1 male 3 female Mangoni. 1 male 4 female Red Top Zebra
. They all do just fine. The reson for over stocking a tank with African cichlids is to keep the aggression down.
I have over African cichlids in my 180 gallon.
Im not saying by any means just put 30 or 40 fish in at one time im saying you need to do your reserch on what fish you realy want to put in your tank. Just remeber that a lot of African cichlids are aggressive.
You will also want a lot of hiding spots for the fish. Like caves holes ect. You can acomplish this by getting rock lick you have mentioned above. I personly use LaceRock. You can buy it online a lot cheaper then at you LFS.
I get mine through Livefishdirect.com I also order my cichlids there to.
If you have questions just ask.
Sorry if i steped on any ones toes.