you guys are more than likely right. it is extremely hard and dense. it maybe in my imagination that it is growing. I do appreciate your responses, thank you. if you all can not tell I am new to this game.
Its a sponge, but its just calcarous. I have a few but they are about as big as nickels. Its harmless, but if it gets too much light algae will grow on it and it will die. If its growing then you must be doing something right. Do you feed any particulate food?