What your lfs is talking about is creating the right water chemistry for Lake Malawi cichlids. They need hard water with a high pH: between 7.8 - 8.9. I use something like this:
http://www.drsfostersmith.com/product/p ... catid=4198
Make sure it is for Lake Malawi fish. When I do a water change, I fill a cup with tank water, add my pH additive, my dechlorinator (I use Prime) and a couple teaspoons of salt. I make sure it is all mixed good then add it when replacing the water. This keeps my water hard and my pH at 8.4.
A Lake Malawi setup is different from any other set-up. They need to be over crowded to a point to reduce aggression. If there are too few fish then there is too much aggression. When you have a bit of overcrowding, the territories overlap and it reduces the aggression levels. You also need to over filter the tank because of the amount of fish. They also need similar aggression levels and the right amount of males to females. ONE male for a group of females. If you have more, the less dominant male will hide and take a lot of punishment from the dominant one.
They also need a lot of caves. A lot of rocks to feel secure. I change mine up every water change. Sometimes I make one long rock pile, sometimes two big ones with the center open. The key is to have enough for each fish to have a cave of its own.
These things are key to having healthy, beautiful African Cichlids. I will walk you thru the steps if you take what I say and do them. OK?
First off, what is your pH?
How many fish are in your tank? It does look like you have way to many for the size tank you have. For a 55 gallon, I would say 18 max. I have 16 in mine.
What fish do you have? And how many of each? Male to female ratio? If you are unsure of what one is, take a picture and we will try to figure out what it is.
It looks like you have a lot of johannii, which is not good unless you only go with johannii. They are one of the most aggressive Mbuna there is and will make the rest miserable.
Have you added more rocks yet? Can you get a picture of the tank as it is now? I also think a dark background on the tank would help too. It looks too bright and open, probably making them skittish.
Lets start with these questions, then walk you thru changes after OK?