How to Choose Aquarium Filtration Media: Biological

How to Choose Aquarium Filtration: Biological

Now that we have covered both mechanical and chemical filtration media, it is time to discuss the final type of filtration, biological filtration. Biological media comes in numerous forms and positively impacts both saltwater and freshwater aquariums.

What is Biological Filtration Media?

Biological filtration media is any surface that provides a place for bacteria to inhabit, grow, and thrive, creating beneficial bacteria colonies that naturally filter an aquarium. Biological media is one of three types of filtration. The other two are mechanical and chemical filtration media which we have discussed in the previous two articles.

Why Use Biological Filtration Media?

Biological filtration is essential to any successful aquarium, whether it be a freshwater, saltwater, or reef aquarium. And unlike chemical and mechanical filtration, biological filtration doesn’t rely on consistently changing or cleaning the media. Biological filtration media takes many forms, from live rock and sand to bio-pellets to bio-balls. This media provides a home, and in the case of bio-pellets a food source, for the nitrifying bacteria that convert harmful ammonia into nitrite and nitrite into nitrate. Nitrates are then removed from the system using a protein skimmer or another form of nutrient export. The better your biological filtration, the more self-sustaining your system will be.

Types of Biological Filtration

Unlike some other types of filtration, biological media comes in many different forms including your rock and sand. Breakdowns of each type of biological filtration are listed below.

Rock & Sand

Image Courtesy of Marco Rocks
Image Courtesy of Marco Rocks

Nitrifying bacteria will populate anywhere with plenty of surface area which live rock and sand have in spades. As a general rule, at least one pound of live rock per gallon of tank water will give you a good start on your biological filtration. Sand also provides a lot of surface area for the growth of beneficial bacteria, however, it can also trap waste and detritus, which is why frequent sandbed siphoning is essential.


Biopellets are small biodegradable spheres. These pellets act as a carbon source (ie food) for beneficial bacteria allowing their populations to grow while improving a tank’s biological filtration capacity. Biopellets are typically run in a media or biopellet reactor and are a great way to add some additional surface area for beneficial bacteria.


Bio Blocks, Cubes, & Balls

Bio blocks, cubes, & balls all maximize the surface area in which beneficial bacteria can populate within your aquarium. These products come in different shapes and sizes to fit numerous aquariums’ unique configurations. The blocks are excellent for large sumps, whereas the balls and cubes make a perfect choice for smaller sumps or all-in-one aquariums.

Biological Filtration Comparison Chart

Type of Media
Bio Blocks, Cubes, & BallsBiopelletsRockSand
How It’s UsedIn a sump or all-in-one aquariumIn a reactorIn any aquariumIn any aquarium
How Long it Lasts2-5 years6-12 months5+ years5+ years
ProsEasy installation, inexpensive, diverse offeringsProvide food source for bacteria, doesn’t require tank or sump spaceLikely already have it in your aquarium, provides a great environment for livestock and bacteriaLikely already have it in your aquarium, provides a great environment for livestock and bacteria
ConsWill break down over timeExpensive to operate a reactor, and biopellets break down over time.Live rock can introduce pests into your aquariumLive sand can introduce pests into your aquarium
Other ConsiderationsWhen swapping in new media, make sure to add it 48 hours before removing the old media to avoid harming the bacteria population.Make sure your reactor has enough flow where all the biopellets are tumbling.Both live and dry rock has large amounts of surface area for bacteria.Both live and dry sand has large amounts of surface area for bacteria.
Biological Filtration Comparison Chart

Final Thoughts on Biological Filtration

Biological filtration media is the best way to provide natural filtration capability to your reef tank. With its use, you can foster the growth of live nitrifying bacteria that aid in the removal of excess nitrite, nitrate and phosphate.

Please contact our support team if you have any additional questions or need a filter media recommendation.

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