Sounds like diatoms, and as rickofco and bertoni stated, this is quite normal. My diatoms started about 15 days or so into my initial cycle. Then I developed cyano, which is also normal for a new tank cycle.
Mine lasted for about a month, maybe a little longer in total. Water changes were a big part in keeping it under control. I also added some phosban to reduce the phosphate in the tank, which is what helps cause the brown algae. I then added a skimmer and this really seemed to speed up the process of getting rid of it. Basically, water changes, picking as much out manually as I could and constantly cleaning my filter pads and filter floss.