There are a few causes to brown algae.
1. As odd as it seems, brown algae can be caused by too little light. Green algae is caused by too much light. Make sure to have your light on at least 8-10 hours. Keeping it on longer might cause green algae to grow, any less may cause brown algae.
2. Over feeding your tank may cause buildup of uneaten food which would be another cause of brown algae. Feed once a day and only the feed amount of food your organisms can eat in a minute. Remember, fish eat about once or twice a week in the wild-shrimp may eat a little more but you really don't need to feed as much as you think you do. Partial water changes can help remove this food buildup.
3. My brown algae problem in my 10 gallon saltwater tank was caused by lack of circulation. I tried cleaning my tank so many times but the problem kept reoccurring. The only movement I had in my tank was caused by my filter creating a circular flow when it poured the water back into the tank. I bought a powerhead to increase the circulation and that definitely helped. I did a water change and wiped down the sides before I attached the powerhead. After I installed the powerhead, the algae did not return. Try to avoid "still water" in your tank. Regardless if you have a fresh, salt, or brackish tank, I would recommend a powerhead!