You now have a MArine Tank, with Marine problems, one of them being a Diatom Bloom. Which in time will take care of itself. Not a long time by the way. If its a brown algae as you describe, and its a dusting all over the things in your tank, its diatoms. The green algae happens also, but for other reasons. What are your phosphate readings? Are yoiu using tap water for your wate changes? If so, your going to get a phosphate reactor and use something like Chemipure to get those phosphates out.