filter media

7.1. Review of Aquarium Filter Media

The first consideration when choosing a filter media is the ammonia-oxidizing capability of the media.

Filter Media Ammonia Oxidizing Capacity

Three tests (24 ninety-day runs total) of the ammonia-oxidizing capability of various filter media were run. All three tests correlated remarkably well. The tests gave an “efficiency” number for various aquarium filter media.

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.

from two tests
surface area
Fluidized K1 medianot tested540na
30 PPI foam17340400
Pot scrubbers1428080
Static K1 media13260200
20 PPI foamnot tested220180
Aquarium gravel6120120
Blue Matala pads5100120
Eshoppe bioballs510060
¼ to ½ inch lava rocks36060
Biohome ultimate24030
Ceramic rings24040
Aquarium Filter Media Test and Efficiency

The higher the number the better the media. So foam is the best static media and ceramic rings are the worst media for canisters by this test and by math calculations. Since foam must be exactly cut to the proper size to prevent flow around pot scrubbers and K1 are much easier to use successfully.

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 .

K1 filter media
K1 filter media
Plastic Pot Scrubbers
Plastic Pot Scrubbers

What this can translate to is illustrated by the number of fish a typical canister can handle stocked with some of these media:

  • Foam

            35 five-inch fish

  • Static K1 media

           20 five-inch fish

  • Ceramic rings, Matrix

           4 five-inch fish

These numbers reflect a canister which will give a hobbyist crystal clear, bacteria-free water which in turn will give one very healthy fish. These are some huge differences.

Click on this link for the test:

7.1.3. Filter Media Test

Yellow Parrot Cichlid
Yellow Parrot Cichlid

Surface Area Calculations

Note that the “surface area foot2 per foot3” is generally based on simple math, not on the claims of the manufacturers. The calculations are:

of pore in
area of a
sphere in
Y =
per inch3
X x Y
Z x 12 =
area foot2
per foot3
60 ppi foam0.0160.0008216,0001732,076800
40 ppi foam0.0250.001864,0001151,380500
30 ppi foam0.0330.003626,000971,164400
1/8-inch gravel0.1250.048051224288140
3/16 gravel0.1880.11114916.5198100
3/8 gravel0.3750.444198.4510150
1/2 inch gravel0.5000.7850863620
Calculating surface area of filter media

The reduction of the figures in the final column reflects the realities of the situation. For instance, only about 40% of the foam cell is surface, 60% of the cell area is void, which allows great water flow but doesn’t give surface area.

These math calculations were tested and the tests generally followed the results of the math. The only significant inaccuracy was that pot scrubbers were much better than the math calculations predicted.

Aphanotorulus ammophilus L 94 pleco
Aphanotorulus ammophilus L 94 pleco

Because of reticulation, flow and free volume considerations the surface area calculations and chart above can be superseded. 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 that should be used for calculating the required volume of filter media for a given weight of fish.

surface area
surface area
inches to
get 5ft²
Cubic inches to get 100ft²
Fluidized K1 media
(60% loading in
30 PPI foam in
canister or sump
30 PPI foam
powerhead operated
30 PPI foam air
operated sponge
Plastic pot scrubbers28031620
Static K1 media26033660
20 PPI foam in
canister or sump
20 PPI foam
powerhead operated
20 PPI foam air
operated sponge
Powerhead operated
undergravel filter
Aquarium gravel in
canister or sump
Air operated
undergravel filter
Blue Matala pads120721440
1/8 inch garden
pumice or perlite
Bio balls100861720
1/2 inch lava rock601442880
Seachem Matrix601442880
Biohome Ultimate402164320
Ceramic rings402164320
Ceramic balls302885760
Expanded clay
Cubic inches to get 5ft² = (5/E.A.)x1,728 100ft²=(100/E.A.x1,728)
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 .

Ammonia Oxidation versus Water Clarity

What is often missed in these calculations is that it is easy to oxidize ammonia. Oxidizing ammonia only requires on the order of five square foot of surface area for one pound of fish per testing and per the literature. However testing and the literature support the fact that crystal-clear water requires somewhere around 100 square feet of surface area per pound of fish. And crystal clear water is healthy, disease-free water.

Blue Dragonblood Peacock
Blue Dragonblood Peacock

Manufacturers’ Claims and Instructions

The claims of many ceramic, pumice and sandstone media manufacturers are based on something called the BET nitrogen infusion method. It measures the amount of nitrogen that permeates a media and adsorbs onto the surface of the media in a single molecule layer.

Since the nitrogen molecule is a couple of billion times smaller than a beneficial bacteria cell this is obviously a very misleading statistic. If a beneficial bacterial cell can’t even get to a surface, let alone form a film on it, the surface is useless. The tiny pores in many media are thus simply of no use.

Another concept that is pushed by manufacturers of some filters is that media needs to be replaced on a regular basis. Some HOB manufacturers say their cartridges need to be replaced every month. There are canister filter manufacturers that say the ceramic bio-rings and the foam in their filters need to be replaced every six months.

This is just ridiculous. Pure and simple profit-motivated Hogwash!!!! Cartridges are easily cleaned when they plug and can be reused for years. Foam will last five to ten years while ceramic or plastic media will last for twenty years or more.

Chindongo demasoni
Chindongo demasoni

Belief Perseverance Effect

Experience on social media has shown that the table above and the testing that produced it will not be believed by 90% of the hobbyists that read it. They will fiercely defend their favorite media (Matrix is probably the single most popular filter media and easily 90% of all biomedia used is either expensive Matrix, Biohome or a ceramic media) and no one will be able to change their minds.

If anything, heavy, slick marketing and the “power of popularity” will make them more intransigent. If presented with test data and logical, common-sense proofs of the data, they will rationalize the experiments away and then rationalize some more. This is called “belief perseverance effect,” something we all fall prey to, and there is no point in fighting it.

“Nothing dies harder than a lie that people want to believe”


The numbers are accurate, and that fact is proven in the links below.

Peacock Gudgeon
Peacock Gudgeon

For more information about filter media click on these links:

7.1.1. Filter Media Costing

7.1.2. Function of Filter Media

7.1.3. Filter Media Testing Filter Media Ammonia Oxidation Test Filter Media Water Clarity Test

Startpage Aquariumscience

Source: – David Bogert

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