I'm having a bit of a brown algae outbreak and I'm not sure what is causing it. I have a 29 gallon aquarium that has been running for well over 3 years. I've not had any fish die, or give any signs of stress. Of course I do 40 to 50% water changes every week. I'm very careful about over feeding and I don't believe my tank is overstocked. I have 4 tiger barbs, 3 gold barbs, 2 odessa barbs and one gold gourami. All fish have been in here for several months (some for up to 3 years) and get along great. From the research I've done, it list the causes of brown algae to the light spectrum changing over time, and to silica. I've replaced my bulb with a full spectrum light and that didn't change the problem. I'm not sure what to do about silica, or if that is the problem. After I clean the aquarium it takes a couple of days, but sure enough the brown algae starts appearing on the glass and especially on decorations. I have not used any chemicals as I'm not sure that would be healthy for my fish. Currently I'm at work so I can't post the exact numbers from water tests, but I can tell you they are all within the "safe" limits. I can post more precise numbers when I get home this afternoon if needed. Any advise would be great appreciated. Thank you.