i add calcium and i havnt checked in awhile what my calcium level is at. I do have coraline on my rocks but not as much as id like. My cousin adds like 5 different supplements and his rocks are awesome looking. His entire back glass of the tank is also covered with coraline. From what i have read, you should add calcium, strontium and carbonate because those are the 3 basic elements found in the ocean that are almost essential for a healthy tank.