7.3. Calculating Filter Media Volume Requirements

If one works all the numbers on biofiltration media in the aquarium filter you come up with two very interesting tables based on volume (cubic inches). The first volume table is based on the well-established fact that ammonia oxidation needs 5 square feet of effective biomedia surface area per pound of fish.

Amount of Biomedia required to give only ammonia oxidation (in cubic inches)

If one wants crystal clear water and healthy fish, ammonia oxidation is only a small part of the story. For heathy fish and crystal clear water one wants at least 100 square feet of surface area per pound of fish. This gives a considerably different table.

Amount of Biomedia required to give healthy crystal-clear water (in cubic inches)

Most of the media numbers represent what a given volume (cubic inches) of media will do stationary in a canister, sump or hang-on-back filter.  We’ve added fluidized bed K1, 30 ppi, 20 ppi sponge filters and an undergravel filter gravel as media in order to give a more complete picture.

It has to be emphasized that these volume tables apply for fish fed at a 1.5% feeding load of typical commercial dry fish food. This is typical for adult fish. Obviously if one uses a  3% feeding (juvenile fish) load will require twice the media. If you feed your fish per the directions on most fish food containers (“what they can eat in five minutes three times a day“) you will need like ten times the volume of media.

Depending on what your goals are for your aquarium, only ammonia oxidation or crystal clear, healthy water, one can now calculate the media needs for any given aquarium. The only missing piece is the weight of the fish.

One surprisingly accurate way to tell the weight in grams is to multiply the length by the width by the height in inches (I know, we’re mixing measurement systems but that’s the rule!). Each calculated cubic inch is very roughly 10 grams of fish. So

• a “normal fish” a five-inch peacock (including tail) is 5 inches by 1.5 inches tall by half an inch wide gives 5×1.5×0.5=3.75   –  3.75x 10=       38 grams.
• A five-inch discus (including tail) which is 3.5 inches high and 3/8ths of an inch wide is 5×3.5×0.375=6.6  –  6.6×10=     66 grams.
• A five-inch fancy goldfish is 5×1.6×1.6=12.8    –  12.8×10=    128 grams.

We will use what researchers have found. Researchers have compiled lists of the weights of very many fish and set up an equation to calculate the weight of the “average” fish. Using the equations and correction factors a table is easily set up for the “average” fish.

The “metabolic” weight reflects the fact that small fish swim much more than large fish, burn up far more calories, and thus give a lot more bioload per gram of fish than do large fish. But note this has to be tempered by the shape of the fish and how active they are.

A wide-bodied fancy goldfish can weigh three times what its length says it should weigh. A slow-moving catfish will only have the actual weight, not the metabolic weight. Surprisingly, tall fish like discus and angelfish are only twice the weight of a similar “normal” fish shape. But also note that long flowing fins like a guppy has have to be ignored in the length calculation. All these considerations makes knowing the actual weight kind of a guessing game.

If one were starting out and put together a typical aquarium with a bottom-to-top flow hang-on-back filter, what would be the minimum amount of each type of biomedia one could have?

Let’s assume the stocking was a community aquarium with three 3″ angelfish, two bristle nose plecos, and one opaline gourami. Because the angelfish are tall one has to multiply 22 by 2. So three angelfish are 132 grams, a 4″ bristle nose pleco is only 21 grams because he moves very slow, and one 4″ opaline gourami is 47 grams. This is 132+21+47 = right about 221 grams.

Let us say you have a bottom-to-top flow hang-on-back with 10 inches by 2 inches by 8 inches of room for media. That is 160 cubic inches (10 x 2 x 8). What will be the media types you can use for ONLY ammonia oxidation with 221 grams of fish? Note the gallons of water and GPH is immaterial.

So the volume chart goes to this:

Amount of Biomedia required to give only ammonia oxidation (in cubic inches)

Ammonia oxidation is EASY and all the media in an HOB will do the job for this 200 gram fish aquarium.

Now let us say that we have the same situation: a bottom to top flow hang-on-back with 160 cubic inches and roughly 221 grams of fish. What is the media which will give us CRYSTAL CLEAR, BACTERIA FREE, HEALTHY WATER?

Amount of Biomedia required to give healthy crystal-clear water (in cubic inches)

That’s right: there is NO media which will give crystal clear water with a typical moderate loading of fish and a typical bottom to top flow HOB filter.

Now since there are at least 12 variables (food level, protein level in food, aeration, etc.) affecting water clarity it is possible to have a very healthy, crystal clear aquarium with this loading and a bottom to top flow hang on back. Possible but not probable.

Doing some other situations:

So let us say you have an aquarium with a fully grown 11 inch Oscar that weighs over 450 grams (about one pound). And you have a large canister with 700 cubic inches (3 gallons, 0.4 cubic feet, 11 liters). What media will give you crystal clear water that will keep hole-in-the-head at bay?

Amount of Biomedia required to give healthy crystal-clear water (in cubic inches)

Per the above only 30 ppi foam, plastic pot scrubbers and static K1 media will give an Oscar complete freedom from the POSSIBILITY of hole-in-the-head syndrome. Note the gallons of water in the aquarium and the GPH are immaterial.

So let us say you have an aquarium with 123 grams of fish. And you have a big canister with 700 cubic inches (3 gallons, 0.4 cubic feet, 11 liters). What media will give you crystal clear water? Per the below most of the media will do that. Note the gallons of water in the aquarium and the GPH are immaterial.

Amount of Biomedia required to give healthy crystal-clear water (in cubic inches)

Again, it has to be emphasized that these tables apply for fish fed at a 1.5% feeding load of typical commercial dry fish food. 1.5% is typical for adult fish. Obviously if one uses a 3% feeding (juvenile fish) load will require twice the media.

An Illustration

Here is a comment to this web page and its answer:

“Paul

I have a 75-gallon community tank with an EHEIM 2217 canister filter.  I’m planning to replace all the EHEIM filter media with Swiss Tropical 20 PPI Poret foam.  I’m thinking of having 5 foam pads, each 2” thick and 7” in diameter.   Would this give me the 220 sq. ft of effective surface area mentioned in your chart?  Using one of your other charts, I calculate that I have 0.75 lbs of fish.    Using the 100 sq. ft for 1 lb. of fish metric, I would think I’ll be able to easily accommodate more fish – is that right?   I’m planning to use your recommendation to squeeze liquid from the existing filter pads onto the new pads to jump start the cycling of the new foam.  How long do you think I should wait before adding more fish?  Thanks for your help.

Dave

OK you have a cylinder ten inches tall and 7 inches in diameter. V = π r² h  π x 3.5 x 3.5 x 10 = 384   This will give one 384 cubic inches of 20 ppi foam. 12x12x12 is 1,728   So you will have 384/1,728 or 0.222 cubic feet. 0.222 x 220 = 49 square feet. So you can do 0.49 pounds of fish at the 100 square foot per pound of fish metric. At the current time you are at (0.49×100)/0.75 = 65 square feet per pound of fish. 65 square feet is good, but it isn’t 100 square feet. So you cannot accommodate more fish.”

And you can add fish right away and just not feed them for a few weeks or wait literally as long as you are comfortable with. I add pond mud (see the article on the “mature aquarium”) and wait at least six weeks minimum but I’m a little nuts.

Another Example of Aquarium Filter Media Calculations

This exchange is from the comments section of this website:

Question #1

“Hi there,
I’m reaching out for some clarity on ‘Square Feet of Biomedia Surface Area’.  I’m considering the 5″ Poret® Foam Sheets (26 × 19.5″ Sheet) and am wondering what the calculations would be for cubic sq. ft.? I plan on executing the ‘10 ft2/gallon of water’ OR ‘100 ft2/pound of fish.’”

Answer #1

“To calculate the volume the math is 5 inch x 26 inch x 19.5 inch / 12 inch x 12 inch x 12inch = 1.47 cubic feet per sheet of Poret® Foam. With a 20 ppi Poret® foam (what I recommend) which has about 220 square feet of effective surface area per cubic foot, this is 1.47 x 220 = 323 square feet. So If you use the whole sheet of Poret® you can support roughly 3.23 pounds of fish in a healthy environment (100 square feet of surface area per pound of fish). And I don’t recommend “10 ft2/gallon of water”. Go ONLY with the “100 ft2/pound of fish”.

Question #2

“Thank you so much for the reply but I’m still confused. Essentially I’m wondering how many – 5″ deep x 26″ long x 19.5″ high Poret® Foam Sheets, will I need for 13.2 lbs. of fish (24 × 8.8 oz Discus or 24 x 8.8/16)?”

Answer #2

“The calculation for 13.2 pounds of fish is 13.2 pounds divided by 3.23 pounds  equals four sheets of 5″ deep x 26″ long x 19.5″ high Poret® Foam”

These examples illustrate the process very well.

Sump Considerations

If one is doing the calculations for a sump one should be aware that fluidized bed K1 is roughly 58% more efficient than static 30 ppi foam as far as filtration. The effective surface area considerations are that fluidized K1 is 900 square feet per cubic foot of media. At 60% loading this becomes 540 square feet per cubic foot of sump filter.

Foam with 30 pores per inch has a surface area of 340 square feet per cubic foot. 540/340= 1.58

Still another illustration:

Question:

How do you calculate the surface area in media used for biological filtration? For example, I have 30 pot scrubbers and some foam in a Fluval 407 canister filter on a 75 gallon tank.

Reply

OK Each pot scrubber is roughly nine cubic inches of media (large pot scrubbers???). 9×30/12x12x12 = 0.156 cubic feet. Pot scrubbers are 260 square feet per cubic foot media (I could be off on that). 0.156x 260 = 40 square feet from the pot scrubbers. If I remember right a 407 has a piece of 30 ppi foam that is 10 inches x 1 inch x 14 inches. 10x1x12/12x12x12= 0.081 cubic feet. Foam is about 340 square feet per cubic feet 0.081×340 = 27.5 square feet. 27.5 + 40 = 67.5 square feet. That is just off the top of my head. You need to correct the numbers depending on the size of your pot scrubbers and the true size of the 407 foam.

Calculations for a pond

A pond requires different graphs and different calculations:

Still another illustration:

Question:

I am planning a pond of approx. 29000 gallons. I have chosen to buy Japanese imported butterfly koi. not bought or created yet as I am in planning mode, and want this right the first time. I will have a k1 fluidized bed, for the main biofilter, and I want to do this for crystal clear water, and super healthy fish…… So if each mature adult koi will end up being ??’8′?? pounds, how many for a heavy stocked 29000 gallon pond, and most importantly how much k1 fluidized? How many gallons of moving k1 should I have for each koi and altogether? I just cant seem to figure it out.

Answer:

You need to work with cubic feet for a pond, It gets pretty big pretty fast. Let us say you want one koi per thousand gallons, or 29 koi. 29 Koi with 100 square ft of surface area per pound is 2900 square feet. So you want 2900 square feet times eight of surface area or 23,200 square feet on your fluidized K1. Each cubic foot of K1 gives roughly 540 square feet. 2900 divided by 540 equals roughly 5.2 cubic feet. Times eight = 43 cubic feet. (alternatively 23,200 divided by 540 equals 43 cubic feet) So you will need a fluidized bed which is 3 foot high 4 foot wide and 3.6 foot deep (three times four times 3.6 equals 43 cubic feet).

Another way to look at it is that an eight pound koi will 8×100 or 800 square feet of fluidized K1. 800 divided by 540 = 1.5 cubic feet of fluidized K1 per koi. 29 koi need 29 times 1.5 or 43.5 cubic feet.

Further Research

For more on how to calculate filter volume go to these articles:

8.8. Filter and Media Design

7.6. Required Aquarium Filter Media Surface Area

Startpage Aquariumscience

Source: Aquariumscience.org – David Bogert