I agree so many different things to try when adding new fish. When I add new fish I no longer turn the lights off. I actually keep the lights on for days. I have recently modified this and now keep 1 light on so the tank has some darkness and some light. The reason being is when the tank is dark all my fish drop down to the bottom and almost guard their own spot. The new fish has no idea where to go and gets picked on all night, as he moves around looking for space. I buy new fish all the time and have found this to be the best for my situation.The question of introduction of African Cichlids can be tricky even with years of experience and with various tanks. The preference is introduction of all fish at the same time ... however that may not be possible or maybe you have an established tank that has lost some fish or you'd like to add a few more. Here are some things you might consider.
• add fish while the lights are out at night
• change the the hardscape, that way all the fish, new and established have something to negotiate
• add fish in a group, if possible different species than you already have
• often adding females is less disruptive
• use a smaller isolation tank to hold a group you want to add, then add them as a group
• use a breeder net box for one or two new fish in the established tank after a week add them to the main tank
Depending on the situation I have one or all of these.