How to Choose an Aquarium Filter Media Reactor

How to choose an aquarium filter media reactor

Filtration is an essential component of keeping a successful aquarium of any type. A filter media reactor can be an excellent tool for efficiently removing many different pollutants and contaminants from the water column. Their low cost, ease of use, and reliability make them essential tools for hobbyists of any skill level.

What is a Media Reactor?

Filter media reactors are containers capable of holding varying types of media, like carbon, GFO, and biopellets. In most reactors, water enters the reactor, flows past the chosen media, and then back into the tank. A media reactor is better than simply placing filter media in a media bag because it increases the contact time between the tank water and the media, increasing the effectiveness of the media.

Nyos TORQ Media Reactor
Nyos TORQ Media Reactor. Image courtesy of Nyos.

How Do They Work?

Most filter media reactors utilize a reverse flow design, pumping water down to the bottom of the reactor chamber before forcing it back up through the media. As the water comes back up, it first passes through a sponge, then through the media itself, and finally through another sponge before exiting and returning to the aquarium. (Do not use sponges when running bio-pellets.) This design ensures that all the water entering the media reactor comes in contact with the media and increases contact time between the water and the media. The proper flow rate through the media is essential, so most media reactors include a flow control valve for controlling the flow of water through the reactor.

Where to Place a Media Reactor

The most common location for installing a media realtor is the sump. The reactor can be mounted or hung on the outside or inside of the sump wall or placed directly into the sump. Most folks install the pump feeding the reactor next to the protein skimmer and return the filtered water into the return section of the sump.

Filter Media Reactor Illustration
Filter Media Reactor Illustration

What Type of Media Can I Use & How to Use It

Although many different media types exist, the most common media used in saltwater aquariums are carbon, GFO, and biopellets.


Carbon is probably the most recognizable type of filter media for aquarium use today.

Why Use It: Carbon’s primary role is removing organic pollutants from the water column. These organic pollutants will eventually break down into nitrate and phosphate if not removed. Carbon also removes inorganic contaminants like chlorine, chloramine, and tannins and improves water clarity.

How Long to Use It: We recommend running carbon from a couple of days to no more than a week per month for a reef tank. Running carbon for extended periods removes essential trace elements and can cause Head and Lateral Line Erosion (HLLE) disease in certain fish species.

How Much Flow: Low flow; the granules should not move or tumble. To further minimize movement, sandwich the carbon media between two filter pads.

Simplicity Aquatics Ultra Carbon Media
Simplicity Aquatics Ultra Carbon Media


GFO or Granular Ferric Oxide is another commonly used filter media.

Why Use It: GFO adsorbs phosphates, silicates, and other chemicals, removing them from your water column.

How Long to Use It: Most folks run GFO continuously; however, it is imperative never to increase or decrease the amount of GFO media quickly. Abruptly changing the amount of GFO will negatively impact the nutrient levels in the tank and stress corals. Replace GFO media when phosphate levels rise, approximately every four weeks for standard GFO.

How Much Flow: Low flow; the top layer of GFO should move or dance slightly. More flow than that, and the media will break down and cloud the display tank water.

Simplicity Aquatics High-Capacity GFO Media
Simplicity Aquatics High-Capacity GFO Media


Biopellets are made from biodegradable plastic. Unlike carbon and GFO that remove pollutants from the water, biopellets act as a food source for aerobic bacteria.

Why Use It: Biopellets provide a carbon source (i.e., food source) for beneficial bacteria within the aquarium. These bacteria, in turn, consume nitrate and phosphate in the water.

How Long to Use It: Like GFO, bio-pellets should be continuously run. Abruptly stopping the use of biopellets will immediately remove most of the beneficial bacteria in the system and could cause the tank to crash.

How Much Flow: High flow; the biopellets within the reactor should tumble. This tumbling action allows the bio-pellets to shed their bio-film. Protein skimming then removes this bio-film from the system.

Simplicity Aquatics Biopellets Media
Simplicity Aquatics Biopellets Media

Sizing Chart

½ a Cup for Every 25 Gallons of Aquarium Volume¼ to ½ a Cup for Every 25 Gallons of Aquarium Volume½ a Cup for Every 25 Gallons of Aquarium Volume
Filter Media Sizing Chart

Alternatives to Media Reactors

Although not as efficient as a media reactor, placing media in a high flow area, like the sump or overflow is a more economical alternative. Liquid additives are also available for nutrient export. These additives remove nitrates, phosphates, and other detrimental elements when dosed into the tank. Another alternative is a hang-on-back or canister filter. Most of these filters allow customization of the media chamber, allowing the user to swap out media depending on their specific needs.


Running a filter media reactor doesn’t need to break the bank. You can get a quality reactor and feed pump for most systems under $100. While there are some reactor models with more bells and whistles, the primary goal of any reactor is to expose your water to the filter media as efficiently as possible.

Filter media reactors are an excellent tool for maximizing filtration efficiency and keeping water parameters in check. Regardless of the type and size of the aquarium, owning a reactor will allow you to attack any nutrient or algae problem head-on. Deploying this tool to improve your filtration will help keep you on track to achieving your aquarium goals.

Please don’t hesitate to contact our support team if you run into any questions or you are in search of a reactor recommendation.