+1 Yote. Having more coraline doesn't really make any difference in the tank other than appearance. I remember back to my first days in the hobby. A LFS told me that when the rocks were covered in coraline, I would know that I was ready to add my first fish. I bought purple up thinking that the algae was in some way helping prepare the tank for the fish, and so I tried to rush it in order to be able to add my first fish more quickly. In reality, he was just speaking to the natural timing of the tank and knew that by the time I started having nice coraline growth, I would be far enough along to properly keep a fish. At this point in the hobby, I don't really see an advantage to accelerating coraline growth and I wouldn't waste the money, not because the product doesn't work, but because it accomplishes nothing useful (unless you just prefer that your rocks are purple) and that's my :twocents: