[vc_row][vc_column css=”.vc_custom_1517703913841{padding-top: 50px !important;padding-bottom: 50px !important;}”][vc_custom_heading text=”High Capacity Granular Ferric Oxide Instructions” font_container=”tag:h1|text_align:center|color:%23515151″ use_theme_fonts=”yes” sub_heading_tag=”h2″][vc_separator style=”double” css=”.vc_custom_1518170834451{padding: 40px 0 !important;}”][vc_column_text]


Granular Ferric Oxide or GFO is an effective method for controlling algae in the reef aquarium, by binding the phosphates which they require for growth, thereby limiting their ability to spread.

Additionally, GFO is also effective at removing silicate which commonly causes brown diatom algae outbreaks in newer aquariums.



High Capacity Granular Ferric Oxide initial dosage rate is 26 grams/100 litres or 13 grams/100 litres standard dose, added via a media bag or fluidised reactor. In saltwater, HC GFO has almost 4x the capacity of standard GFO so a half dose is possible. Additionally, the media has the potential to last 4x as long at full dose.



  1. Pour High Capacity Granular Ferric Oxide into the bag and close securely
  2. Rinse with RO water or place under a faucet until the water runs clear
  3. Place in a high flow area of the tank or sump to maximise water flow through the GFO
  4. Change the media when phosphate levels rise or algae growth becomes visible (4-8 weeks)



  1. Place HC GFO in a suitable reactor, such as the Dual GFO & Carbon Media Reactor
  2. Place the reactor’s return line into a bucket or sink
  3. Turn on the feed pump to flush the fines from the GFO until the water runs clear
  4. Place the return line in the tank
  5. Reduce the flow through the reactor so the GFO barely tumbles on the surface.
    Do not allow the material to vigorously tumble.
  6. Change the media when phosphate levels rise, typically 4-8 weeks.



IMPORTANT: If any negative coral reaction is noticed after adding or changing High Capacity Granular Ferric Oxide, reduce the amount by half. While overdosing is unlikely, dropping phosphates too quickly can cause shock to an established aquarium.

Monitor aquarium phosphate level & add or change media when levels start to rise, or if algae increases. Sometimes algae can consume so much phosphate that tests will show low or no phosphate while algae growth is still present. After the first 2-3 weeks, continue increasing the amount of Granular Ferric Oxide until algae is controlled. For optimal effectiveness, do not allow overall Phosphate levels to test above 0.05ppm.

Pro Tip: Test water coming directly from the media reactor for phosphates. If any phosphates are present, High Capacity Granular Ferric Oxide should be replaced or dosage rate increased.



To make sure your reactor stays clean and free from detritus, it is best to pre-filter water going into the reactor. It can also be useful to add a small check valve to the pump side of your water line and keep the return line submerged to prevent back siphoning into in the event of a power cut.

Check weekly for good flow and fluidisation. If clogged, dump reactor contents into a bucket of tank water, stir and pour off detritus. Media can then be returned to the reactor in part or whole. Pro tip: Use this technique when changing media, and save approximately 1/4 of the old media to mix into new media, keeping bacterial cultures stable to prevent bacteria or algae blooms. If used in a canister filter, use a micron bag to hold the Granular Ferric Oxide, preferably in thin layers to ensure good even flow, and reduce channelling through the media.

Exhausted media will not leach phosphates back into the aquarium water.


For a downloadable copy of these instructions, please visit the User Manuals & Downloads page.[/vc_column_text][/vc_column][/vc_row]