Brown is a diatom norm when cycling a new tank. Are you dosing ammonia, or using a raw table shrimp, or ghost feeding to cycle your tank? Now that you been up about a week i would start testing for ammonis, nitrite, and nitrates. Look for ammonia spike and its fall off to zero, also the spike and fall off of nitrites. When that occurs nitrates will begin to rise you then should do a water change and get a clean up crew, ie hermits, emerald crabs, snails in then give a week or two then you can add one or two fish but go slow to allow your bio filter to be able to compensate and keep up.