From everything I've seen, I think it actually has more to do with unstable conditions in a newer tank than silicates. I know a lot of people have mentioned silicates, but I haven't seen any real evidence to show that water high or low in silicates has any effect on it. According to any hard evidence I've seen, for silicates to actually etch out of glass into solution, you have to have a solution with an extremely high pH (like 10). I have been able to induce brown algae just by doing a major water change and vacuuming out the gravel really well, causing the tank to re-cycle somewhat. The brown algae always goes away after the tank restabilizes. This is why I think it has more to do with some type of microorganism that does something in the tank once it's established that prevents this type of algae.