If in doubt, purchase a really nice piece of live rock with corralline algae already on it. Place in the tank and use a toothbrush to scrub it. This will seed the already placed rock. But, as the previous poster said, give it time and it will come back. Keep up with the water changes to give the tank new water, and before long you will see changes. Good luck, looks like a nice start. What size tank is that?