I'm not sure I can add much more over what you have already got replies wise in the tank. Anyone that keeps mbuna will know that it's actually hard to get algae growing as they constantly graze it, being veggie lovers. I would say your lighting period is too long and really not as important for mbuna.
Regarding plants technically it would be better if you didn't have any just rocks, as that is a better natural setup for them. You could try java moss but I've seen mbuna eating it before now. Why do you want plants in your tank anyway? I would concentrate more on providing plenty of rockwork and hiding places, if you get the chance to look at a book called The Natural Aquarium by Satoshi Yoshino and Doshin Kobayashi there is a fantastic mbuna setup in there.