most likely brown diatom algea. You get it in every new tank setup and it fades in time. Ways to help keep it under control: High flow, low nitrates, and low phosphates. It can take days up to a month before it disapears for good. Soon after will come the green algea. Once you get a bunch of brown and/or the green starts growing is the time to add cleanup crew members.
Diatom bloom, it will go, just keep a check on the nitrate/phosphate levels in the tank. I've had the same thing even though all i've done is moved my 2 year old live rock straight from one tank to another, saltwater aquariums just don't like being messed with.
Yep diatoms. This is a bacteria/algae that feeds on the silicates within the sand and water. Once these silicates are used up it disspears as a new and higher form of algae out competes it.
You'll find that you get it popping up if you do a massive water change or add new sand, anything that contains or leaches silicates, etc. that's why my tank's got it even though the live rock is fully mature.