Malawi cichlid illness

It started all after i introduced a new rock and a plant in my Malawi
tank.
After a while(3-4 months) my Pseudotropheus zebra died with black
spots on their heads,then the same happened to the livingstoni; now I
have the Melanochromis auratus and 5 leleupi with the same black
spots.
I would like to know what can cause this?
Now I have the survived fishes in a different tank, whereas the
original tank is empty.
How I have to clean the infected tank, the rocks and the sand?
Can I put again the same cichlid fish in it, once it is clean, or
maybe all will start up again?
There is a way I can cure my fishes?
Thanks for any help

Andrea (Italia)

Here's a picture of one of my sick fish:
http://spazioinwind.libero.it/unaltr...eb/ciclide.jpg

Sorry, but I uploaded a bad file... now clicking below you can see the right
ill fish, just look at the black spots in the head!

Andrea (Italia)

Here's a picture of one of my sick fish:
http://spazioinwind.libero.it/unaltr...eb/ciclide.jpg

I have Red Zebras "Pseudotropheus zebra" that has develped black 1 mm wide spots on the right side, in the back half of the fish. Did you ever learn what it was or how to heal your fish? It was a long time ago that you posted this thread.

Hello Andreea.
There is a solution to your problem. Try to find K Mn O4 and put it in your aquarium until the water became pink. The fish and the plants are kept separately. The pink color must be kept two hour to be sure that all organic substances are neutralized. Then put your filter to work until the water became cristal. Change 50% and put back your plant and fish.