We make two types of GFO, standard and high-capacity.  As the name implies, our high-capacity media can hold more phosphate. The material is denser and requires less media to get the job done. You will experience lower dust (cleaner) and less likelihood of the media compacting inside your reactor.

When using GFO for the first time, it is not uncommon for the first batch to exhaust quickly because of initial elevated phosphate levels.  Monitor phosphates closely with a test kit and swap out the GFO media as soon as levels begin to rise, sometimes as soon as 7 days.  After the first batch is swapped out, the following batches of GFO will last much longer, typically in the 4-8 weeks range as described below.


Standard BRS Granular GFO: A cost-effective solution for everyday phosphate control

  • 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: High-density, long-lasting, lower-maintenance phosphate removal

  • 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: Recommended

  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 or Granular Ferric Oxide is designed to remove phosphate from the aquarium water. It can be used as a tool or treatment to lower elevated phosphate levels but is also safe for everyday use in aquariums with a heavy bioload where phosphate levels cannot be managed by other means of filtration.

Each tank is different and unique in terms of the ideal phosphate level. We find that most tanks ranging from 0 to 3 years old should be maintaining a lower phosphate level between 0.01 - 0.04 PPM for the best results. 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 phosphorous is required for fish, corals, and beneficial bacteria to grow and thrive in your reef tank, it should not be allowed to stack up in the aquarium water as a byproduct. 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. You don't want to starve your tank of phosphate altogether, but you also cannot let rise out of control.

Elevated phosphate levels often indicate an elevated nutrient level altogether.  This means nitrate is likely on the rise as well and you should be mindful of your bioload. Nutrients like this can contribute to the growth of nuisance algae and various other pests (cyanobacteria, dinoflagellates, etc). Science also tells us that phosphates can inhibite calcification among corals, meaning it will limit their growth at higher concentrations. Conversely, if your tank is stripped of phosphate altogether, you can encounter bacterial imbalances and starve your corals and other critical organisms of necessary phosphorous.

The main source of phosphate is going to be fish and/or coral food and the resulting waste. Additives and media can also contribute, but the amount will often be negligible compared to what your food is bringing in. Managing filtration that helps remove leftover food and fish waste is your primary focus for phosphate control, should that not suffice, Bulk Reef Supply GFO filter media is our favorite tool. 

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.