My Mbuna tanks (5) have been running for years with a few shallow (maybe 3") rock piles at each end. I do have caves using pvc pipes/clay pots. I have never experienced an aggression problem. Psaulosi,labs and perlmutts are the fish. I know they are in their natural habitat "rock fish". I've personally found less aggression in my tanks with less possible " territories. So this morning cleaning tanks. Diatoms have always discolored everything in my tanks. Before advising all the causes.....I've tried everthing. I have high phosphate in our city tap water. I believe that's my problem. Couple years ago I gave up scrubbing my rocks. Sick of doing it they have been brown/black since. Don't like that. Also don't any fry. Can't give hem away. Also I'm looking at decreasing number of tanks as I just reached 78 yrs. Long story to ask does anyone have no rock work tanks?