If one works all the numbers on biofiltration media in the aquarium filter you come up with two very interesting tables. The first table is based on the well established fact that ammonia oxidation needs 5 square feet of effective biomedia surface area per pound of fish.
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.
Most of the media represent what a media will do in a canister, sump or hang-on-back filter. We’ve added 30 ppi and 20 ppi sponge filters and an undergravel filter gravel as media.
It has to be emphasized that these 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 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 the rule!).
Each calculated cubic inch is 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.
|Length Inches||Length Centimeter||Weight Grams||Metabolic Weight Grams|
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 nosed 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 nosed 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 you can use for ONLY ammonia oxidation with 221 grams of fish? Note the gallons of water and GPH is immaterial.
So the chart goes to this:
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?
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.
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?
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 canister with 700 cubic inches (3 gallons, 0.4 cubic feet, 11 liters). What media will give you crystal clear water? Per the below all media except Biohome and ceramic rings will do that. Note the gallons of water in the aquarium and the GPH are immaterial.
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.
Here is a comment to this web page and its answer:
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.
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:
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.’”
“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”.
“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)?”
“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.
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:
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.
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.
There are some aquarium hobbyists who are interested in delving deep into the science and the calculations behind all aspects of the hobby. For those who are so inclined the following is pertinent: