I have a brown algae that has shown up in my tanks. I do not have co2 going on any tank as of right now I do however add a dose of flourish to my planted tanks @w/c. I have a 75, 10, and a 7 gallon planted tank that has this same issue. I believe it came from a lfs. I have cut the light cycle down a 1/2 hour on the 75 and 10gallon. The 75 has HE 67000k 28w that was on for 8 hours. The 10 has a 60w that was on for 8 hours. The distance of the light has also been moved to a foot from the top of the tank. The 7 gallon has a led light that is on about 8-9 hours. Non of the tanks are near a window and there is a weekly 25% w/c. Any input is great and I would like to stay away from chemicals.