Brown algae or diatoms are from minute levels of ammonia in the tank, usually present in a new set up. The ammonia will not show on a test kit and usually disappears on it's own after a few weeks. It can smother plant leaves so you may want to restrict the light to 6 hours a day, avoid direct light from windows and don't over feed your fish, plus, gently brush the algae off(it will look like a dust in the water when you rub it off). It will sort out on it's own. The fluffy stuff on the drift wood sounds like a harmless fungus from the wood and will also go away on it's own. Shrimp, oto's and catfish seem to like to browse it.
