Brown algae

Hey guys, it's Twoface again. In some of my previous posts I explained I bought a 20 gallon saltwater aquarium that was established for over a year. I got about 17 gallons of the original water and added 3 gallons of fresh mix. It came with. 20lbs of live rock, 30lbs of live sand, 3 coral and no fish. It's been set up for 3 days now and today I noticed some brown algae starting to cover the sand. I'm new to saltwater aquariums so I need some help. I did a 10% water change today and filtered up as much algae as I could. Any tips as to how to get rid of the algae and keep it gone. I've been doing about 9 hours of light for the coral a day so far. They seem to be doing great and my button polyps have even added another polyp since Saturday morning. Thanks and please help!