I take care of a 55 gallon freshwater aquarium in the nature center where I work. Recently I changed the substrate. It seems that started a bad chain of events. I have a lot of brown algae. I did some on-line research and got conflicting answers. I think the brown algae is caused by diatoms. But how do I get rid of it? It looks ugly and I just lost another plecostomus. The only species that seems to be surviving are my black tetras. I'd appreciate any advice.