Simplicity GFO (granular ferric oxide) which has the ability to bind phosphates making them harmless. High phosphate levels in a reef aquarium cripples coral growth and fuels algae. Using GFO to bind the available phosphates leads to improved coral health, coloration and reduced algae growth. While it is recommend to be used in a media reactor with a gentle tumble, it can also be used in a media bag placed in an area of high flow. Available in 1 lb. and 20 lb. sizes.