Im curious as to what this is. It only grows on this rock, doesnt spread to anywhere else and nothing will eat it. I had the normal outbreak of algae in my tank when I cycled ,but the week after I put my clean up crew in everything was gone except this. It does constantly get bigger but not at a super fast rate. My tank is 4 months old at this point. I dont really want to get rid of it as it kinda adds a more natural look and color to the tank. Just interested to see what it is.