Seachem Matrix filter media

7.2.12. Seachem Matrix filter media

Seachem Matrix is a “natural rock” product that is heavily marketed by Seachem as a supposedly extremely good media to be put into aquarium filters. Matrix is NOT good media for aquarium filters. It has the following shortcomings:

  • Low effective surface area which gives poor biofiltration
  • Sheds small abrasive particles that take out pumps
  • Does not do any denitrification
  • Very high cost

Ceramic media like Matrix have a huge amount of false marketing hype and snake oil salesmanship. It is all false. Matrix does NOT have huge amounts of beneficial bacteria living inside it. We go into the reason behind that in great length below. Only hobbyists who are nerds like the author need to read on. This is VERY long and boring.

Matrix in Depth

Matrixtm is a whitish-gray half-inch “natural stone” biomedia product that many hobbyists swear by. It is probably the most common media in use in the hobby. It is made by Seachem.

Note I admit that I have a “chip on my shoulder” when it comes to Seachem products. The amount of misleading and downright false marketing hype that Seachem uses for ALL its products is just nauseating. And they have threatened me with a libel suit. I do not like being threatened. Just for information purposes, one cannot be sued for libel or defamation if one simply tells the truth. Which I have done in all cases.

Matrix Media of old (note the variability and the obvious stone on the right)
Matrix Media of old (note the variability and the obvious stone on the right)
New Matrix Media (much more uniform, with no stones)
New Matrix Media (much more uniform, with no stones)

Matrix is very similar to porous ceramic products in all its properties. It is extremely expensive with very little effective surface area (about 20 to 40 ft2/ft3).

Pseudotropheus elongatus
Pseudotropheus elongatus

Note that it appears that Matrix was changed several years ago. Years ago Matrix was obviously pumice, a type of volcanic rock that doesn’t absorb water and floats. Matrix of old had variable composition stones in it and obviously was mined from a rock pit. The MSDS (material safety data sheet) for Matrix identified it as Pumice.

The new Matrix is identical in appearance (under a microscope!) and properties to a man-made fused glass product that used to be available in garden stores called “Growstone”. Matrix now absorbs water and sinks, just like Growstone. Hhhmmmm???

Note that one could purchase the “Growstone” material for 10% of the cost of Matrix. Also note that as of 2019 “Growstone” was renamed “Buddystone” for some reason.

There is another aquarium filter media available in some countries like India called  ADA bio Rio media. This is virtually identical in all its properties to Matrix, except the product is sold wet, supposedly seeded with beneficial bacteria. This product claims to have enough beneficial bacteria on it that it can “instantly cycle” an aquarium. These claims are just marketing hype. Like Matrix, it is extremely expensive with a high profit margin. Thus every fish store in India “highly recommends” it. LOL Love the profit motive!

SP Super Red Ruby Peacock
SP Super Red Ruby Peacock

False Marketing Claims

The surface area claims made for Matrix are 700 meters per liter. This is  700,000 m2/m3 or 213,416 ft2 per ftof surface area. As usual with Seachem this is a mix of truth and lies, in a masterfully word-smithed narrative.

Per a very complicated test called the BET nitrogen infusion test, Matrix may well have the “surface area” it claims to have. But this is incredibly misleading. This surface area claimed for Matrix is based on how much nitrogen gas can penetrate the media and adsorb on the surface via something called a pycnometer via a complex calculation called the BET equation. This test doesn’t even come close to reflecting reality in the aquarium.

Matrix has roughly 15 to 30 ft2/ft3 of EFFECTIVE surface area, confirmed by testing under actual aquarium conditions. The BET test gives 213,416 ft2 per ft3. And the math and real-life testing give 15 to 30 ft2 per ft3. How’s that for marketing hype?

Enneacampus ansorgii African Pipefish
Enneacampus ansorgii African Pipefish

The difference here is largely due to the difference in size between a nitrogen molecule and a beneficial bacteria. The nitrogen gas molecule is billions of times smaller than a beneficial bacterial cell. So, the nitrogen gas is adsorbed in billions of tiny pores where bacteria can’t even fit. Since it is the bacteria that do the oxidation of ammonia to nitrate, Matrix is MUCH less effective than its marketing hype would indicate.

Depending on the ceramic process used, the pore size in ceramic media such as Matrix can be as low as 0.0001 microns in size. The ceramic media claiming the highest surface area have the smallest pore sizes. A bacterium is 2 to 5 microns in size. So the BET nitrogen infusion test is simply worthless in determining the surface area available for beneficial bacteria to colonize.

Also nitrifying bacteria live inside a biofilm (which they create) and that has a thickness of around 50-300 microns (let’s say 200 microns average). So, a round pore inhabited by nitrifying bacteria is coated on all its internal surfaces by this film. This means that a diameter of around 400 microns (almost half a millimeter) is occupied by bacterial biofilm. And then, enough space needs to remain for a good water flow through it. This means that a single pore needs to be larger than at least one millimeter (two is even better) to be efficiently occupied by nitrifying bacteria.

Glass catfish
Glass catfish

Also, let’s say Matrix with its large surface area will have a “large” pore size on the order of 30 microns (one-thousandths of an inch). A bacterium is 2 to 5 microns in size. So, a bacterium only must divide a few times to clog a “large” passageway into Matrix. Bacteria can multiply every 30 minutes. Think about that for a while. Even the “large” pores are just too small. They clog far too rapidly. The actual effective surface area of Matrix after a few weeks is on the order of only 15 to 30 ft2 per ft3.

There is no way to sugarcoat it. Seachem’s surface area claims are simply bogus. They are pure unadulterated marketing hype.

In any case, the other problem with Matrix has to do with flow. For nitrifying (ammonia-oxidizing) beneficial bacteria to work there has to be a high flow over the surface of the bacteria. The flow with Matrix is around, not through the media. So the Matrix media will do a very poor job of biofiltration, even if the beneficial bacteria could somehow manage to fit into the structure of the Matrix.

The proof that beneficial bacteria do not live inside Matrix is simple. After a few months of operation, beneficial bacteria turn brown. I took a piece of Matrix that had been operating in a canister for years. It was brown all around the outside. When I split it in two with a chisel the inside was pure white, with not a hint of brown. There was no bacteria inside the piece of Matrix. NONE!

German Red Peacock
German Red Peacock

Testing Matrix

A test was run on filter media which showed Matrix had about one-fifth of the ammonia oxidized capability of foam on a cubic inch to cubic inch basis. It had about one-fourth the capabilities of static K1 and pot scrubbers.

A test of the 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.

from two
Surface Area
from Math
30 PPI Foam17340400
Pot Scrubbers1428080
Static K1 Media13260200
Aquarium Gravel6120120
Blue Matala Pads5100120
Eshopps Bio Balls510060
1/4 to 1/2 inch
lava rock
BioHome Ultimate24030
Ceramic Rings24040
Filter biomedia efficiency

The higher the numbers here the better the media. This makes 30 ppi foam the best media and ceramic rings the worst media.

This test makes it clear that the claims of huge surface areas by Seachem are simply very misleading. But this is typical of Seachem. More details on the test can be found at this link:

7.1.3. Test of Filter Media

Copadichromis borleyi OB
Copadichromis borleyi OB

How Does Matrix Stack Up?

A comparison is in order. This table compares K1 extruded plastic media to Matrix media as static biomedia in a canister filter or sump filter.

PropertyMatrixtmK1 type
plastic media
Cost per ft3 in bulk$ 200$ 50
Surface area in ft2/ft330200
Cost per 100 ft2
surface area
$ 666$ 25
Does it shed abrasive
Is it used by most
to fill their canisters
Comparison of Matrix and K1 Media

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

So Matrix costs four times more than K1 on a volume basis and a given volume of Matrix only can handle one-sixth the load of a given volume of K1. This is a difference in cost-effectiveness of a factor of 24, which is huge.

Belief Perseverance Effect

The social media response has shown that many, many hobbyists who read this analysis that have Matrix in their filters will simply reject the above testing and analysis. This is something called “belief perseverance effect”. It says that when we buy something, especially if we pay a lot of money for that something, even when presented with the evidence we made our purchase in error, we tend to rationalize and support our decision. Logic and science will often have little effect on such beliefs.


Now ignoring the science and embracing Matrix will not kill one’s fish. They will only result in what is an unnecessary expenditure of money and possibly some less-than-healthy fish. If one believes in Matrix, have at it! In our society burning money is completely acceptable.

Startpage Aquariumscience

Source: – David Bogert

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