As Rendos said, RO/DI helps. Regular water changes will control a build up. To not introduce them is the goal. They come from, food, fish waste, replacment water and even some salts. If I had to guess, most peoples comes from overcrowding and overfeeding.
A natrul defense is always the best. A DSB has been shown to work. Plenums have also been shown to work. I belive that regular maintance is the best way to control it.
Live Rock and lots of it is what I depend on.