Can I use this rock and death coral in my aquarium?

http://img398.imageshack.us/img398/7729/pict0829qe0.jpg

PS: I have used it for over two years, but I stopped the aquarium because of the fish deaths (they were dying a lot, i don't know if it was because of the rocks, I think it was because of the food, because I was using a automatic fish feeder).

Now I begun the aquarium with sucess. but I don't used this rocks, which are very beautiful on water.
The aquarium is a tropical fish tank