As a novice, many of us can be overwhelmed with everything you need for your journey into the hobby, let alone the terms hobbyists use for these things. Well, we're here to break down one of the common terms thrown around, filter media. Filter media is needed in almost all aquariums and has a few sub categories which each have a specific use. So, here's a little beginner's guide to filter media and how to use it.

Mechanical Filter Media

Close up shot of a filter pad

Mechanical filter media, the main form of filtration for most aquariums, includes filter rollers, filter pads, filter socks, sponges or anything that captures free floating particles of waste. Some forms of this media are denser than others, making it tougher for smaller particles to go through. This density is measured in metric form, microns, where 1 micron is equal to 1/1000mm. A really dense pad or sock of 50 micron will capture finer particles in comparison to one that is 100 micron.

How to use Mechanical Filtration Media

  • Mechanical filtration in most cases the first form of media in contact with the water in the filter.
  • Depending on density/pore size, filter pads should be changed about once a week.
  • Most mechanical filter media can be reused, like sponges and filter socks, after a rinsing and dry; check out How to Clean Filter Socks.

Beginner's Guide to Carbon Filter Media

Close up of carbon filter media

Carbon is probably the most widely used media (after mechanical) in aquarists' filtration system. It can sometimes be found packaged with new power filters as a cartridge insert or even included in a bag with AIO (all in one) aquariums. But what does it do? Carbon will pull things such as chemicals, medications, organic compounds, odors and other impurities out of the water, when used correctly. This in turn clears the water, allowing better light penetration for any photosynthetic livestock and better viewing for us.

How to use carbon filter media:

  • Before use, rinse the carbon with RO water or from the aquarium during a water change to rid it of any dust particles.
  • Carbon should be used in a ratio appropriate to your tank size, per manufacturer recommendations. Example: 1/2 cup for every 40 gallons of water volume.
  • Replacing carbon should be done every 4 weeks or as needed.
  • In sump use: carbon can be placed inside a filter media bag, then placed in an area of high flow where water can actively pass through it, like in between a baffle.
  • In a fluidized media reactor is probably the most efficient way to use carbon. This increases the contact time with water. Just note that some media reactors will require extra plumbing and a feed pump.
  • In a power filter there is usually a slot that the carbon cartridge slides into. If not a media bag of carbon can be stacked with the filter pad

Beginner's Guide to GFO (Granular Ferric Oxide) Filter Media

Close up GFO/Phosphate filter media

GFO media is probably second in popularity among aquarists. This media helps remove phosphates introduced by fish food, fish waste, impure water and many other ways. By removing phosphate, GFO greatly reduces one of the primary nutrients that allow nuisance algae to grow and source of coral growth inhibitors. However, there is a fine balance when keeping this nutrient in control; we don't want to remove all phosphates in the water as it would take away from zooxanthellae in coral which also use it.

How to use GFO:

  • GFO should be rinsed before use with RO/DI water or using aquarium water from a water change to rid the media of any dust releasing into the tank
  • GFO, like carbon, should be used in a ratio appropriate to your tank size, per manufacturer recommendations. Example: 1/4 cup for every 50 gallons of water volume
  • In a media reactor with a low flow pump, the media can gently fluidize and tumble for better contact time
  • Testing phosphates will let you know when to change the media as needed, otherwise should be done about every 4-6 weeks.

Beginner's Guide to Chemical Filter Media

Close up of all-in-one media which includes chemical filtration media resin

Chemical aquarium media refers to a media that chemically interacts inside the aquarium, and not a chemical additive. One of the most popular types of chemical media is an ion exchange resin, like Seachem Purigen or in all-in-one media like Chemi-Pure. Ion exchange resins work a lot like carbon media as it absorbs (or adsorbs) organic waste compounds, reducing ammonia and clearing up the water while ignoring trace elements.

How to use Chemical Filter Media

  • Chemical media can be used in a filter media bag, if it is not already packaged in one, and set in an aquarium filter or sump for water to actively pass through.
  • Some ion exchange resins have the extra benefit of being able to recharge their effectiveness, like Blue Life Regenerable Resin or Seachem Purigen is that it can be recharged and used again.
  • Chemical media can last up to 6 months but should be replaced per manufacturer's recommendations or test results.

Beginner's Guide to Biological Filter Media

Bio filtration blocks and biopellets examples.

Having bacteria in our aquariums is how our tanks are able to keep toxic levels of ammonia and nitrites from killing our livestock by denitrification. Cycling a fish tank uses bacterial growth to consume fish waste and convert ammonia to nitrite, to nitrate, and onto nitrogen gas. Having a steady population of this denitrifying bacteria is key to keep the tank running and a good way to make sure you have a steady population is with bio media such as media blocks or biopellets.

Biofilter media blocks, balls and ceramic rings are a few choices for biofiltration and can accompany live rock in marine tanks to give it a boost. This media is highly porous giving bacteria plenty of real estate to colonize and get to work. The porosity of it also allows for better water penetration that brings in the nutrients the bacteria need.

Biopellets are a plastic media composed of biodegradable polymers that provide a shelter for bacteria. The bacteria utilizes nitrate and phosphates in their biological processes as they feed on the carbon-based pellet itself. As the bacteria begins to thicken as a film on the pellets and will eventually shed as the media tumbles, exposing new surface area for it to colonize again. The shed bacteria is then filtered out by a protein skimmer or consumed by filter-feeding inhabitants.

How to use Bio Filtration Media:

  • Media bricks, plates, cubes, etc. can be placed in any open area within a sump or filter where water can actively pass through and around it.
  • Biopellets must be used in a media or biopellet reactor with a pump with enough flow to gently tumble the pellets.
  • Prior to use, biopellets should be soaked in aquarium water over 24 hours or longer until they're no longer floating.
  • Biopellets should be added slowly starting with approximately 25% of the recommended amount, then adding the same amount each week thereafter.
  • The outlet of the biopellet reactor should be directed towards an efficient protein skimmer, which will cause more skimmate production.
  • Phosphate control media should be reduced to allow biopellet bacteria cultures to grow as they require traces of phosphate.

Final Thoughts

Swapping out filtration on a regular basis, knowing what media to use or what media you don't need can be a little overwhelming for many beginners. Having a routine and balance in filtration is another aspect to keeping aquariums thriving. So, keep in mind not all the media discussed in this article is needed, and do recommend finding your tank's balance through water testing and observation.

If you have any questions about filter media, please feel free to contact us at or by calling 714-385-0080.