New tank? It is most likely forming on particles of uneaten food or on driftwood. To get rid of the first type, cut back on feedings. The second type will just go away on it's own. I've noticed this in new tanks and on new pieces of driftwood. It's normal, not harmful, and usually takes care of itself. It might me a good idea to siphon it out if it is forming on uneaten food as this can degrade your water quality.
You'll have to be more specific on the brown gunk. Diatomaceous algae maybe? Brown, patchy scum on glass that wipes away easily? Again, common to new tanks. The growth rate will go way down as the tank matures.
.....wait, I am seeing into your tanks future......I see....yes, its a bloom of green hair algea........
You'll go through several kinds of algae blooms as your tank matures. If you keep up weekly water changes, you'll eventually end up with green spot algea that grows at a very manageable rate.
Good Luck, and Welcome to AC!!
Of course you could be an experienced hobbiest with a fully mature tank in which case I'll look like an idiot. Wouldn't be the first time
