Using GFO in a Phosphate Reactor

May 24, 2016
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  1. Determine the amount of GFO needed. Start with 2 grams of per gallon of water in the system. After a few months the organisms in the tank will have adjusted to the lower phosphate environment. At this time the amount of Granular and Pelletized GFO can be increased to 3-5 grams  per gallon of water. Please note that these amounts are suggested starting points. As each tank is different, it may be necessary to vary the amount used for better results.
  2. Rinse the GFO. Place the GFO in the reactor and return to the tank. Remove the return line on the reactor from the sump or tank and place in a waste bucket. Turn on the reactor to rinse the material. Once the water runs clear place the return line back in the tank.
  3. Adjust the flow rate. Once the GFO is rinsed adjust the water flow by turning the ball valve on the reactor. There should be just enough flow so the GFO gently tumbles. This will prohibit the GFO from forming one big chunk. If the media is tumbling to vigorously the particles will grind against each other and create small fines that will be released back into the tank.


The phosphate reactor you purchased can be used before your RO DI system or can also be used to filter the water out of your aquarium utilizing a sump (Maxi Jet 1200), through the reactor, and into a reservoir to be pumped back into your aquarium thus eliminating the phosphates that cause algae growth.


Which GFO should I buy?

 High Capacity Granular.


  • High Capacity Granular (HC GFO)is our premium GFO, and comes with several distinct advantages over the other GFOs. HC GFO is able to remove roughly twice as much phosphate as the other types. This means it will last longer and require less maintenance. The particles are extremely hard and even better than the Pelletized GFO at reducing the effects of water abrasion. HC GFO works very well in both a reactor and filter bag. If you are going to be using a filter bag with your GFO, this is the preferred product.
  1. I use GFO. Why do I still have algae issues?

Algae needs three main nutrients to grow: Phosphates, Nitrates and light. Reducing any one of these will significantly slow down algae growth, but rarely cause it to completely die off.

Once algae takes hold, it can be extremely difficult to remove. The best offense against algae is to take preventative measures and attack before an outbreak is apparent. Use the following suggestions and be aggressive if an algae problem is already present:

  • Control undetectable nutrients with GFO
  • Only use RO/DI water for water changes and auto-top off*
  • Practice good feeding habits and shorten lighting periods.
  • Remove as much algae as possible by hand.
  • Add predators. One of the best ways to control algae is by adding critters that like to eat it. Buy twice as many snails and crabs as you think you need.

Good habits like these will aid in solving current algae issues as well as help you prevent an outbreak.


You ought to change out the GFO once it is full and no longer able to remove any more phosphate.  It is going to vary drastically from person to person. It is strictly contingent on the live stock you have, how often you feed, what you feed, how much you feed at a time, what your water change schedule is like, etc.  It is very possible for one person to add ten times as much phosphate than another.

It is recommended that you start with changing every other month and adjusting accordingly.  If you find that this isn’t keeping up with the amount of phosphate you are adding to the tank, then you should change it at a greater frequency.  If you feel like you are a particularly heavy feeder, or use foods that you know are high in phosphate, then you should start by changing monthly.

  1. I mix my GFO with my carbon should I still let it tumble in the reactor?

Absolutely not. The GFO is harder that the carbon and will grind it to dust if you allow the particles to grind against each other 24/7. There is also no benefit to the tumbling if used with carbon. The tumbling is to prevent the GFO particles from attaching to each other and forming one giant rust ball. There is no need for this if the partials are not touching each other because of the carbon.

  1. How aggressively should the GFO particles tumble ?

Slower the better. The slow tumbling action stops the particles from attaching to each other and forming one big rust ball. However the tumbling action also grinds the particles against each other and creates dust. So you want to set it as low as possible to prevent them from solidifying and at the same time minimize the abrasion between the particles.

A typical wet GFO weighs 75 pounds per cubic foot and our Standard dry GFO weighs 29 pounds a cubic foot. Both have essentially the same phosphate removing capacity on a volume basis, thus it requires  2.6 times as much wet GFO to treat an equivalent amount of water.

  5.How does wet GFO differ from dry GFO ? (GFH vs GFO)

  There are two main granular iron based medias. Granular ferric Hydroxide (GFH) is a wet product and Granular Ferric Oxide (GFO) is a dry product. 

The products are extremely similar and in an aquarium environment there is going to be very little difference worth noting. Price and capacity should the primary motivating factors when purchasing for your aquarium.

The following is information provided by our supplier and relates to these products main application .

GFO/GFH is primarily used in the municipal water supply world as a tool to remove arsenic.  The following are the benefits they feel their dry product has over the competitions wet product (GFH).

1) GFH is very heavy because of the water weight and costs more to ship. This results in the client paying nearly 50% more in freight costs.

2) GFO granules are physically more robust and less prone to physical attrition/loss.

3) GFH shelf life is considerably shorter because being wet; it is prone to decomposition and loss of surface area. Metal oxides produced and stored as wet products are gelatinous and prone to decomposition.

4)  GFH can freeze in cold climates and mold in hot climates, GFO does not have either of these issues.

5) GFO is a crystalline form of iron oxide whereas GFH is mainly an amorphous form of iron oxide. The crystalline product has more consistency in terms of adsorption capacity and shelf li