GFO or Granular Ferric Oxide is designed to remove phosphate from the aquarium water to maintain healthy and stable levels of phosphate for optimal tank health. Each tank is different in terms of the recommended phosphate level but most tanks ranging from 0 to 3 years old should be maintaining a phosphate level between 0.01 - 0.04 PPM for the best results. We find that more mature aquariums that have been established for 2 - 3 years or more with large mature coral colonies can often run with higher levels of phosphate input without issue.

While phosphate is required for corals to grow and thrive in your reef tank, elevated levels can lead to nuisance algae problems and inhibit the growth of coral. Managing phosphates is all about balance and stability, finding the right level that works for your particular tank, and not allowing the levels to constantly rise.

GFO is one of the best ways to provide ongoing phosphate management and maintain those stable levels.  As the media becomes exhausted, phosphate levels will begin to rise as indicated by your regular water testing and you know it is time to replace the media. 

Standard BRS Granular GFO

  • Start with 1 tablespoon per 4 gallons of water
    (16 tbsp = 1 cup).
  • After 4-8 weeks the aquarium will have adjusted to lower nutrient levels and the amount of GFO can be increased up to 2 tablespoons per 4 gallons of water.

BRS High-Capacity GFO

  • Start with 1 tablespoon per 8 gallons of water
    (16 tbsp = 1 cup).
  • After 4-8 weeks the aquarium will have adjusted to the low nutrient level and the amount of GFO can be increased up to 2 tablespoons per 8 gallons of water.

For Use In A Filter Media Bag:

  1. Pour the GFO 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 maximize water flow through the GFO
  4. Test phosphate levels regularly and replace the GFO media when phosphate levels begin to rise (typically every 4-8 weeks)

For Use In A Upflow Media Reactor:

  1. Place GFO in a suitable media reactor
  2. Place the reactor's return line into a bucket or sink
  3. Turn on the feed pump to flush the fines/dust from the GFO until the water runs clear
  4. Install the media reactor on your tank and place the return line appropriately into your sump or filtration
  5. Reduce the flow through the reactor so the GFO barely tumbles on the surface. Do not allow the material to vigorously tumble.
  6. Test phosphate levels regularly and replace the GFO media when phosphate levels begin to rise (typically every 4-8 weeks)

GFO, Phosphates, and Algae -What you NEED TO KNOW

GFO will not solve an algae outbreak by itself. If an algae outbreak is apparent, attack it head-on with a multi-prong defense specific to the type of algae you're dealing with. Here are some common ways of helping defend your tank against nuisance algae growth. Algae is a natural part of keeping an aquarium and incorporating these methods into your regular routine will ultimately help you avoid problems with excessive algae. 

  • Manual removal and cleaning of algae-covered surfaces
  • Use GFO or other methods to maintain low phosphate levels
  • Add utilitarian fish and clean up crew animals such as tangs, blennies, snails, and crabs
  • Shorten lighting periods or perform a blackout period
  • Maintain a more efficient water change schedule and proper filter maintenance
  • Maintain and tune your protein skimmer
  • Monitor the tanks nutrient input via fish and coral foods

Learn more by checking out our video The 5 Minute Guide to Fighting Algae In Saltwater Aquariums.