Hello and thank you for your inquiry.
For a 29 gallon tank you have quite a few fish in the aquarium. I would recommend taking the tang out of the tank as they require much larger tanks.
I have linked a couple of articles below that should help with the maintenance that should be done on a reef tank. The brown stuff is more than likely some type of algae or diatoms. If your water quality is good (ammonia, nitrite, nitrates and phosphates at zero, pH ~8.0-8.4, calcium 380-420, alk 9-12 dkH) and you are using filtered water for topping off from evaporation and making new saltwater for water changes I would recommend increasing water flow within the tank and also possibly running some type of phosphate remover in the tank (like Phosban in a phosban reactor).
If there is anything else we can do for you please let us know.
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