7. Filter Media

A Confession

The author would like to be able to say he knew what this testing revealed all along and has been using 100% foam, pot scrubbers or K1 in all his many canisters over the 53 years he has been keeping aquariums. That would be a lie. For some 45 years the author had used a combination of all the media that came with a canister, a ton of a huge variety of media which was on his garage shelving, and media he bought. Most of his canisters were filled with a pretty random combination of Matrix, ceramic rings, lava rock and bioballs.

The author simply felt that the media in a filter wasn’t very important and they were all pretty much equal. The author was wrong, dead wrong. Whoops!

OB Peacock
OB Peacock

I think a comment by one of the readers of this website is apropos now:

“After reading through many of the various articles you confirmed what I suspected for many years regarding ceramic media. I always had a nagging suspicion that biofilm was found predominantly on the surface (not internal pores) of all this expensive media I have purchased. My suspicions were confirmed earlier this month when I foolishly replaced all of the outer foams on both my FX6 filters. The filters’ internal baskets were filled with “high quality” spherical sintered glass media which should have housed all of the beneficial bacteria but the tank had a tremendous bacterial bloom after that sponge replacement which made me think that the outer sponges were housing a significant portion of the bacteria. I stumbled across your page a few weeks later and was kicking myself.

I have since replaced both FX6 filters with two Eheim filters which combined hold 4 gallons of media. I owned Eheim filters in the past but it got rid of them because I fell for the “maximum tank turnover” provided by the large FX filters based on youtuber claims (mistake). I gradually swapped media and filled the two new Eheim filters with Kaldnes media in a static configuration and I’ve been monitoring parameters and the water quality is great (zero ammonia and zero nitrite). I opted for Kaldnes as a static media over 30ppi sponge to avoid early clogging in an African cichlid tank holding 25 fish between 2 and 3 inches long.”

To see what this commentator is talking about just read on.

Nimbochromis livingstonii
Nimbochromis livingstonii

What is the “Best” Filter Media?

What has to be emphasized here is that most people key in on only ammonia and nitrite oxidation when looking at filter media. If a canister filled with lava rock gives zero ammonia and zero nitrite than the lava “works fine”. Ammonia and nitrite oxidation requires very little from a filter media. So media like lava rock “works fine”.

What is being missed is the concept of crystal clear water. That is water so clear that if you look down the length of a six foot aquarium you would think the fish are swimming in air. Crystal clear water requires twenty times more surface area that does ammonia oxidation, confirmed by controlled testing.

And the need for “crystal clear” water goes beyond aesthetics. Fish which are in crystal clear water will almost always be very healthy fish that don’t get diseases. This is because crystal clear water is very clean water. The cleaner the water the healthier the fish.

So the choice of which filter media to use just boils down to a personal choice depending on what one wants from their aquarium. An aquarium with no ammonia and unhealthy fish OR an aquarium with both no ammonia and crystal clear, healthy water. The choice is up to the hobbyist.

image of an aquarium fish Cyphotilapia frontosa Tanganika Moba
Cyphotilapia frontosa Tanganika Moba

Abstract of a Filter Media Tests

A series of some six tests were run on the capacity of filter media.

  • To test the ammonia oxidizing capability of various aquarium filter media  10 five gallon buckets were set up. The filter media was put in ten air operated corner filters. This test was replicated three times (thirty tests total) and replicated well. The testing data correlated well with the mathematically calculated effective surface area of each media. In turn the ammonia oxidation ability of the media by surface area correlated strongly with six research literature references on ammonia oxidation surface area.
  • Clarity of the water was measured for eight weeks of cycling ten 40 gallon aquariums with different filter media in canister filters and a heavy load of food. Two full tests and one partial test were run. This was a total of 25 tests using canisters and aquariums. The second test used half the media that the first test used. The third test used twice the media of the first test. These tests largely confirmed that crystal clear water requires some twenty times the filter media effective surface area that ammonia oxidation requires. These tests with aquarium and canister filters also largely confirmed the first tests with buckets and corner filters with regard to the ranking of various media.

This was a total of 55 tests of media. All the tests correlated well with foam, pot scrubbers and K1 media significantly outperforming ceramic rings, Matrix and Biohome in ALL the tests.

These tests showed:

  • A typical large canister filled with 30 ppi Poret foam (“sponge”), static K1 media or plastic pot scrubbers will give good ammonia oxidation with 700 five-inch mbuna and crystal clear, healthy water with 35 five-inch mbuna.
  • A typical large canister filled with ceramic rings, lava rock or BioHome filter media will give good ammonia oxidation with 80 five-inch mbuna and crystal clear, healthy  water with 4 five-inch mbuna.
Otopharynx tetrastigma
Otopharynx tetrastigma

Media Ranking and Selection

One very important decision to make in the area of filtration is what media to use in the filter. In many ways this is more important than choosing a filter. The most important function of the media is ammonia oxidation.

A test of ammonia oxidizing capability of various filter media was run. The first number, the “efficiency” is the average ammonia oxidizing that 15 cubic inches of media accomplished over a 90-day period. The second number is the “effective” surface area in square feet per cubic feet calculated from that test. The third number is the effective surface area in square feet per cubic feet calculated by simple mathematics. The correlation between the test results and the calculated surface area is very significant and means the testing was accurate.

filter biomedia efficiency
filter biomedia efficiency

Note that for the metric system simply multiply any of the square feet per cubic feet numbers by 3.3 to get square meters per cubic meters. For the metric system 100,000 f2/f3  thus equals 330,000 m2/mor 330 m2/l3 .

The higher the numbers here the better the media. This makes 30 ppi foam the best static media and ceramic rings the worst media for canisters. The complete test procedure used to come up with these numbers is outlined in the following link:

7.1.3. Filter Media Test (links to aquariumscience.org)

Oxyeleotris marmorata Marble Goby
Oxyeleotris marmorata Marble Goby

Because of reticulation and free volume considerations the surface area calculations are not very dependable. Extrapolating from the testing and giving aquarium gravel the most dependable surface area calculation, gives the following “effective surface area” by media. This is the surface area which should be used for calculating the required volume of filter media for a given weight of fish.

filter biomedia efficiency
filter biomedia efficiency

Note that for the metric system simply multiply any of the square feet per cubic feet numbers by 3.3 to get square meters per cubic meters. For the metric system 100,000 f2/f3  thus equals 330,000 m2/mor 330 m2/l3 .

Note that the fluidized K1 media is for the volume of the sump, not the volume of the media in the sump. I.e. 540 sq. ft of effective surface area per 1 cu. ft. of volume containing K1-media AND water (in the dedicated sump chamber, with 60% K1 loading. Another way to say this is: (540/0.6) = 900 sq. ft of effective surface area per 1 cu. ft. of “dry” K1-media, when the “dry” K1-media is put in a fluidized sump chamber with 60% K1 loading.

Note that a fluidized K1 bed with 60% loading of K1 has, on a cubic foot of filter volume, a little more than twice the biofiltration capability of static K1 media. This makes the cost per square feet of biofiltration of fluidized K1 to be only 30% of the cost of static K1. This makes fluidized bed K1 a VERY cheap media when purchased in bulk.

Super Blue Hybrid Peacock
Super Blue Hybrid Peacock

Mixing Media

Most hobbyists do an interesting thing. They mix their media. It is not uncommon to see eight types of media in a sump or six types of media in a canister. Since all biomedia do exactly the same thing, namely provide surface area for beneficial bacteria to grow, this is just rather humorous. But EVERYBODY does it, including the author prior to doing this testing!

Since the media with the greatest surface area is also the media which will plug up the fastest, this use of many types of media can be counter productive. For instance, if a hobbyist has some 30 ppi foam in a canister filter along with some Matrix, bioballs and ceramic rings.  The 30 ppi foam clogs at four months. so the hobbyist takes apart the filter and cleans ALL the media. Cleaning the Matrix, bioballs and the ceramic rings is decidedly counter productive.

Aquarium Fish Protomelas taeniolatius Red Empress OB
Protomelas taeniolatius Red Empress OB

Marketing Hype about 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 in order to make money. These falsehoods are spread around social media by well intentioned but mis-informed 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”.

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.

Panaqolus albivermis L204 Emperor Pleco
Panaqolus albivermis L204 Emperor Pleco

The links below are a complete review of all the filter media, discussions of each media in depth, the calculations needed to work out how much media one needs for various situations and discussions on media which just don’t work as advertised:

7.1. Review of Filter Media (links to aquariumscience.org)

7.2. Individual Filter Media (links to aquariumscience.org)

7.3. Calculating Required Media Volume (links to aquariumscience.org)

7.4. Chemical Filtration Media (links to aquariumscience.org)

7.5. “Denitrifying” Media (links to aquariumscience.org)

7.6. Aquarium Filter Media Surface Area Requirements (links to aquariumscience.org)


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Translated in dutch by : Joost Abrahams
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