The rock is super neat but very dense to the point that it has very little biological filtration properties. It would basically consider my tank void of LR if I had only this in the display. But I would load up the sump with "real" LR for filtration. You also have to be careful of rock contaminants. They an leach stuff like iron. I am going to have mine tested before use (if I go that route) but a simple sample could still miss the presence of contaminants. I would soak the rock in saltwater over a period of time and test for release of anything impurities. They could be a pain in the booty much like a plastic plant would be. I'm not sure.