What does GFO do exactly and why do I need it?

GFO or Grandular Feric Oxide (rust) is used in a fluidized media reactor to remove phoshates from your aquarium water.  Phosphate is the number one killer of aquarium coral and phosphate is also a major cause for algae blooms in our aquarium.  Just like weeds in a garden, algae used phosphate as a fertializer.  Controlling phosphates on a continual basis is one of the key elements to maintaining a beautiful saltwater aquarium.