1.1.6. Filter Media

Filter Media

Filter media is the stuff inside a filter. It is something that grows beneficial bacteria on its surface These beneficial bacteria remove fish pee (ammonia) from the water. Filter media is important to the health of the fish. The more effective surface area this media has and the less the media is cleaned, the better the health of the fish will be.

Trichopodus leerii Pearl Gourami
Trichopodus leerii Pearl Gourami

One Big Scam

Any discussion of ANY filter or filter media requires a disclaimer. ALL commercial filters almost without exception tell the owner in the directions to replace the filter media (Cartridges, sponge, ceramic rings, carbon, Matrix, etc.) regularly, once a month, once every three months, or once every six months. Supposedly this is because the media becomes clogged and dirty. And the media is ridiculously expensive. We must emphasize:

Replacing the Filter Media is a Big SCAM!!!

Yes, there is absolutely no reason to replace the media regularly other than to make a lot of money for the supplier of the filter.

Lemon Tetra
Lemon Tetra

Cartridge Filters

Cartridge filters have a plastic frame that typically has a fuzzy cloth “bag” or “cover” and black granules of activated carbon inside the fuzzy cloth bag. These filters are the most common type of filters sold for small tanks.

Hang-on-back Filter Cartridge
Hang-on-back Filter Cartridge

If one has only a cartridge filter (either in tank or hang-on-back), you have only the activated carbon in the cartridge to act as biofiltration media. It is important to ignore the directions and never replace the carbon. Just get it all filled with brown gunk. If carbon is filled with brown gunk it is a decent biofiltration media.

To improve a cartridge filter, simply replace the cartridge with foam blocks. One can get these foam blocks from Cory at Aquarium Co-op. Cory also has a great YouTube video on how to do this. To understand this improvement better, click on this link:

8.2. Hang-on-back Filters

Brochis splendens Emerald Cory
Brochis splendens Emerald Cory

“Brown Gunk”

The single biggest mistake beginners make is to think that the “brown gunk” that builds up in their filters and substrate is fish poop and must be cleaned away as often as possible. This “brown gunk” is a very well-ordered structure that does a huge amount of good in the aquarium. It contains beneficial bacterial colonies which keep the ammonia down and keep the water crystal clear.

When a newcomer to the hobby cleans this media thoroughly they will typically either get an ammonia spike or cloudy water. And they will post on social media “what happened to my tank?”. What happened is that they just removed their beneficial bacteria and they will have to recycle their tank. We tested this with sponge filters and confirmed that thorough cleaning is not a good thing to do, especially with a newly cycled filter media. This is a link to the test:

6.8. Thorough Cleaning

The biggest myth about filtration is that one needs a clean filter for the filter to be effective. Exactly the opposite is true. The dirtier the filter media the better the filtration.  The filter below filtered an aquarium with perfect water parameters and some very healthy fish. It was not a “nitrate factory” nor a spewer of disease pathogens.

A Well Functioning Aquarium Filter
A Well Functioning Aquarium Filter

Myths and Marketing Hype on Filter Media

Filter media are very important in a fish tank. But there are a huge number of falsehoods about filter media spread by equipment manufacturers to make money. These falsehoods are spread around social media by gullible fishkeepers. These falsehoods include:

  • Purigentm creates crystal clear water and removes ammonia, nitrite, nitrate, and toxins from aquarium water.
  • Matrixtm, BioHometm, sintered glass media, and porous ceramics (blocks, balls, rings, noodles, etc.) are the best biofiltration media with huge amounts of surface area on which bacteria can grow.
  • Some ceramic media (De*Nitratetm and BioHometm) remove nitrates by anaerobic decomposition to nitrogen gas.
  • Activated carbon, exchange resins, zeolites, and chemical filtration media (i.e. Chemi-Puretm and Poly-Filtertm) are very useful in the freshwater aquarium.
  • Filtration media (cartridges, bio-rings, foam) needs to be replaced every month or every six months or “when they get dirty”.
  • Foam is a mechanical filtration media and not a biological media

These claims are all just marketing hype easily debunked. But these claims do serve the purpose of making a lot of money for some creative aquarium supply manufacturers and distributors.

Pethia conchonius Rosy Barb
Pethia conchonius Rosy Barb

To go into the subject of filter media in more depth click on the following link:

7. Filter Media


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Translated in dutch by : Joost Abrahams
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