From FrugalReef

Diatoms are the most common form of phytoplankton. They are also refereed to as microalgae, brown or golden algae. Diatom blooms are common in new tanks but are usually not long lived because they quickly get taken over by other kinds of algae. Diatoms require silcates to grow, these most often enter the aquarium through tap water. (Silicates can not come from silca sand, silica sand does not dissolve in water and is for all intents and purposes as completely inert as glass because it is glass)

[edit] See Also

• Algae Control
• http://saltaquarium.about.com/cs/algaecontrol/l/blpicalgaediato.htm - Pictures