i had the same problem until recently. i have a replaced one of my blubs with a coral light bulb. i purchased some live rock with purples on it and "most importantly" i started using coral vite. this stuff not only gets the live rock growing, it promotes new growth on dead rocks. they brown algae has gone away and now i have purples, greens, blues and reds. it took about 3 to 4 weeks after treating. give it a shot. it is kinda expensive.
otto