New and encountering a problem

Hey folks. I am new to this hobby. I have had my 30 gallon tank up and running for a few weeks now. Have aragonite substrate and 10 pounds of live rock so far. Will be adding around 20 pounds more live rock this week. My sand and rock has brown furry stuff on it. I'm hoping it's diatoms and not something worse. Anyway how do I get rid of this? I added snail's and hermits about a week ago and they aren't doing anything. Any help is much appreciated