I use a combination of natural colored sand on top and crushed coral beneath that. I must say that the sand makes it more entertaining since the fish will dig their own territories out. they also will sift through the sand to try to eat any uneaten scraps. one thing I regret is that I bought play sand to try to save money when I set the tank up and I really wish I went with pool sand. The play sand cannot be rinsed enough and months later, I still have clouding after WC b/c the particles in the play sand are so fine. Spend the extra money for pool filter sand since it doesn't cause this problem