GFO and activated carbon are both types of filter media used for removing waste from an aquarium, so should you use one or the other or both? Although they both remove waste, they are used at different stages of the waste removing process… active carbon removes organic matter while GFO primarily removes phosphates… and as such it can be beneficial to run both in a reef aquarium.
What is GFO used for and the pros / cons of using it?
GFO filter media is used in reef aquariums for removing phosphates, silicates and other chemicals from the water. Chemicals are attracted to the surface of the GFO by the process of adsorption whereby they are safely and effectively removed from the water. Even as the media is exhausted or used up it will not release the adsorbed chemicals back into the water column.
Pros of Using GFO
- Safely removes phosphates, silicates and other chemicals
- Readily available
Cons of Using GFO
- Removes trace elements
- Remedy: Routine water changes or dosing of trace elements
- Can reduce alkalinity / pH
- Remedy: Gently tumble media in a reactor or turn media in filter media bag to prevent it from clumping together.
- GFO dust is damaging to fish and coral
- Remedy: Carefully rinse prior to use and do not aggressively tumble the media
- Removing phosphate too quickly
- Remedy: Start with small amounts of GFO
What is Active Carbon used for and the pros / cons of using it?
Active carbon is used in reef aquariums for removing organic pollutants and other toxins from the water. Just like GFO it works through the process of adsorption.
Pros of Using Active Carbon
- Adsorbs organic waste like fish food, poop and other detritus
- Adsorbs contaminates like airborne solvents and some heavy metals
- Adsorbs odors, organics and tannins which yellow your water
- Adsorbs toxins caused by chemical warfare between corals
Cons of Using Active Carbon
- Adsorbs some beneficial elements like iodine, aminos and medications
- Remedy: Routine water changes or dosing
- Poor quality carbon can release phosphates and organics
- Remedy: Use a high quality carbon, like Simplicity Ultra Carbon
- May cause Head and Lateral Line disease or HLLE (Scientifically unproven, but widely believed)
- Remedy: Use a reasonable amount of product to reduce the risk
When should I use GFO, Carbon or both?
This is a bit like asking if you should change your oil in the car on a regular basis or add fuel to your car. The short answer is that they are both important tools in waste removal as they are generally used to do 2 very different things; GFO is generally used for removing phosphates while carbon is mostly used for removing organics and toxins.
Below is an infographic demonstrating the waste cycle and how excessive food, fish waste and dead items are processed in your aquarium. This graphic shows how waste is removed from an aquarium and where different filtration methods are typically utilized in the process.
Infographic: Waste Removing Process
An efficient protein skimmer and effective mechanical filtration generally reduces the need for using GFO and active carbon, however both still play a key role in most reef aquariums and together all 3 create a great team for removing waste from your aquarium.