Too much light duration will cause your tank to produce algae...I had the same problem, wanna know what I did put a real plant near an area with too much algae and guess it all dissappeared, another factor that may cause you to have algae is the position of your tank, if it is close to a window that will be another reason!
They are just a different type of algae. Brown algae tends to be more annoying because I'm pretty sure no fish will eat it. Just buy an algae scrubber/scraper/pad, whatever they happen to call it, and scrub it off. Don't use chemicals to kill algae...they are harmful to fish and a lot of the time don't work.
The "brown algae" is pretty normal for a tank that is only a few months old. They are called diatoms, and usually disappear on their own after a month or 2. You can speed up the process by exposing the tank to more light. Otocinclus love the brown stuff and can clean your tank sometimes within 24 hours.