GFO comes in two types:

• Granular GFO is varied in its shapes and requires the least amount of flow to tumble. Good for reactors.
• High Capacity GFO is twice as dense as Granular GFO, so twice as much material will fit into a reactor. It's extremely hard and has less dust to begin with. Fewer fines will be created during use and transportation. By volume High Capacity GFO will remove roughly twice the phosphate compared to Granular GFO. Best overall performance.

Special note on fighting existing algae problems: Algae needs three main nutrients to grow: phosphate, nitrate and light. Reducing any one of these will significantly slow down algae growth but many not completely solve your issue. Once algae takes hold, it can be a difficult battle but it is winnable. 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:

• Maintain undetectable phosphate levels with good feeding habits and use of a phosphate remover like GFO.  99% of all phosphate is added via foods added to the tank.
• Control nitrate levels by reducing feedings, increasing the water change schedule and maintaining a properly sized protein skimmer.
• Use nutrient free RO/DI water for water changes and top off water
• Shorten your lighting period or intensity. In some cases aquarists have found replacing old bulbs that have fallen out of their intended spectrum helps as well
• Continuously remove as much algae as possible by hand.
• Add predators nothing helps an algae outbreak as much as critters who eat it all day long. Various tangs, lawn mower blennies, crabs and snails are all good options. It is also theorized that a healthy pod population will also control algae growth before it gets a chance to take root.