With all of the different types of filter media available for our aquariums, choosing the right kind can be extremely confusing.

When keeping a reef aquarium, it is especially important because using the wrong media or using it the wrong way can have some pretty nasty effects on your tank.

Carbon, GFO and BioPellets are currently the most popular types of filter media, and for good reason: they are inexpensive, easy to use and proven to help keep your aquarium water clean, clear and free of impurities. Keep reading to learn precisely how these different types of filter media benefit your aquarium and how to use them correctly.


Activated carbon is the most widely used type of filter media and the benefits of using it are pretty amazing. Carbon effectively removes medications, organics, chemicals, color contaminants, odors and other impurities from your tank.

Most hobbyists use activated carbon at all times, but it can also be used situationally to remove medications or chemicals. In fact, many of the medications and algae treatments on the market recommend the use of activated carbon to help remove any residual chemicals from your aquarium after the treatment is complete.

Many of the corals we keep inside our reef aquariums release toxins into the water as a form of defense. Carbon removes these chemicals from the water column which allows hobbyists to successfully care for a variety of corals. With regular use, carbon can help you achieve crystal clear water. With better light penetration and less dissolved organic waste in your aquarium, fish and coral are more likely to thrive. Carbon also keeps your tank from stinking up the house—which should make your family or roommates happy.

The best way to use carbon is to fluidize it inside a media reactor with moderate water flow. Adjust the flow so the carbon is tumbling and slowly "boiling" on top. Carbon can also be effective when placed inside a filter media bag and dropped into a media basket, canister filter, sump or hang-on power filter. Just rinse before putting it into your tank and place it where water will constantly flow through it.

Under normal circumstances, carbon should be replaced every 3-4 weeks. When used to remove medications or chemicals, you'll want to swap out the carbon after only a few days since it will become exhausted rather quickly. It is important to note that leaving carbon in your tank for too long can cause problems. It is important to change your media regularly. If you do not have extra carbon media available, just remove the carbon from your tank in the meantime until you do.

GFO (Granular Ferric Oxide)

GFO, or Granular Ferric Oxide, is pretty magical stuff. GFO filter media is one of the best defenses against algae outbreaks and lasts a surprisingly long time when used properly.

Phosphate is the leading cause of nuisance algae in aquariums. It also inhibits the growth of calcareous corals. An elevated phosphate level may even cause your prized SPS corals to brown out or perish.

Phosphate enters your aquarium mainly through fish waste, but also via supplements, food and even top-off water. GFO binds to the phosphate in your aquarium water making it unavailable to fuel algae growth or adversely affect your corals.

You can use GFO filter media at all times in any reef tank. Fluidizing the media inside a reactor yields the best results. It helps prevent clumping and ensures maximum contact time with your aquarium water. Adjust the flow inside the reactor so the top layer of GFO is "simmering." You do not want it to tumble or move too fast. Higher flow may turn the media into a fine dust which could potentially be released into your aquarium.

GFO media must be thoroughly rinsed before it can be placed inside your system. Testing your phosphate level regularly will let you know when it is time to replace it. In short, if you see your phosphate level begin to rise, it is time to swap out your GFO for fresh media. In an aquarium with elevated phosphate, GFO can become exhausted in a matter of days. Once phosphate has dropped to an acceptable level, a single batch of GFO can last for months.


Last but not least, we have BioPellet media.

BioPellets have become more and more popular with reef aquarium owners in recent years. They work in conjunction with a protein skimmer to remove nitrate from your aquarium. They have a small effect on phosphate, too, but you should still run GFO since BioPellets are not really an effective way to control or reduce your phosphate level.

The way BioPellets work is pretty cool. The pellets are made of an organic-based plastic that acts as a food source for bacteria. As bacteria grows on and consumes the pellets, nitrate in your aquarium is also consumed. The bacteria colonization on the pellets soon creates a "biofilm." As the BioPellets tumble inside a reactor, the biofilm sheds off the pellets carrying with it the bacteria and nitrate. The film is then removed by your protein skimmer and the nitrate along with it.

You can't use BioPellets without a BioPellet reactor. Adjust the flow into the reactor so the pellets gently tumble. Place the effluent or outflow from the reactor in close vicinity to your protein skimmer intake or plumb it directly to the skimmer intake for best results. This allows the skimmer to remove the biofilm immediately after exiting the reactor. When running BioPellets, you will likely need to empty your skimmer cup more often and clean your mechanical filters more frequently as well to prevent them from becoming clogged.

It is important to note that it takes time for the bacteria to grow, so be patient and be sure to keep the pellets tumbling. It generally takes 4-6 weeks for a BioPellet reactor to start working effectively. You should slowly introduce your system to BioPellets, starting with a ½ or even a ¼ of the recommended amount for your aquarium size. As time goes on, you can slowly add more pellets until you reach the full recommended amount. This will minimize the shock to your system from dramatic changes in nitrate levels. You will need to replenish the pellets as they become consumed over time. Using a full dose right off the bat can cause a sudden change in water chemistry and really shock the animals in your aquarium. It is crucial that your protein skimmer is working properly because without it, the nitrate and bacteria film cannot be removed from your aquarium water.

Filter media is fundamental part of keeping a healthy reef aquarium. If you questions about filter media, please leave us a comment or contact us! Our staff of experts is always happy to talk tank and share our experience with you. Don't forget to subscribe to our YouTube channel to stay up-to-date on all the latest aquarium news.

Until next time, take care and happy reefkeeping.

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