How Many Fish Can I Have In My Pond?

Professor Russell the Koi How many fish can I have in my pond?

How Many Fish
Can I Have In My Pond?


To accurately answer that question it should be rephrased as:
“How much ammonia can my filtration system process?”

Average Fish Weights and
Pond Stocking Levels

To Use The Chart Below Correctly:

    SSA = Milligrams of ammonia your biological filter can process
    Milligrams of ammonia processed X 5 = Weight of fish that produced it
    Divide the fish weight by the length and number of the fish in your pond = How many, and what size fish you can have in your pond


There are many “non-truths” out there discussing the topic of “How many fish can I have in my pond?”. Virtually all them refer the number of fish per gallon of water and/or the surface area of pond. Water volume does not process the ammonia the fish produce …. that’s the job of the biological filter. Ammonia as low as 0.25 ppm is toxic to pond fish and koi. The biological filter is critical for the removal of the ammonia your fish produce. The most accurate way to know “How many fish can I have in my pond?” is to know how much ammonia your biological filter can process. All biological filters produced by Russell Watergardens & Koi list the SSA and fish weight it can support in the gallons specified.

The most important aspect of the pond and how many fish it can support is the filtration system. The bottom line is this: Fish poop and release ammonia into the water. More fish …. more ammonia. Also, the bigger the fish …. the higher the proportion of ammonia it produces. The filtration system has to process the ammonia and filter out the poop to keep your fish alive, happy, and healthy. See the Fish Weight chart below to see how the ammonia produced by fish increases exponentially with the size of the fish.

How many fish can I have in my pond? SSA = milligrams of ammonia processed

The Pond Filtration System for Fish Ponds of All Types Include:

  • Mechanical stage filter that removes the physical fish waste
  • Biological stage filter seeded with nitrifying bacteria to process ammonia
  • Circulation of at least 100% of pond water volume through the filtration system every 3 hours
  • Dissolved oxygen level at least 7 mg/l

  • Fish produce 1 milligram of ammonia per 5 grams of body weight per day.

    Example: 500 grams of fish produce 100 milligrams of ammonia per day.
    Fish produce ammonia from:

  • Gills
  • Urine
  • Feces

  • Ammonia
    Biological filter SSA = Total milligrams of ammonia the filter can process in 24 hours.
    Example: 100 sq. ft. of Nitrifying Bacteria bio film Specific Surface Area (SSA) processes 100 milligrams of ammonia per 24 hours.


    How many fish can I have in my pond? SSA = milligrams of ammonia processed

    Incorrect Calculations
    for “How many fish can I have in my pond?”

  • One 6″ fish for every hundred gallons of water
  • 1″ of fish per 10 gallons of water
  • Total gallons of pond divided by 200 = Total 6″ fish in pond
  • 1″ of fish per square foot of pond surface area
  • Example: 12″ of fish
    Twelve 1″ fish produce a combined 0.60 milligrams of ammonia (12 X 0.05 = 0.60)
    Six 2″ fish produce a combined 2.70 milligrams of ammonia (6 X 0.45 = 2.70)
    Two 6″ fish produce a combined 23.70 milligrams of ammonia (2 X 11.85 = 23.70)
    One 12″ fish produces 95.03 milligrams of ammonia all by itself.

    As you can see, using the size of fish per gallon of water cannot be accurate as the ammonia increases exponentially as the fish size increases. Size of fish per volume of water calculations do not address the filtration system. The biological filter is the engine of the pond. Without knowing how much ammonia the filter can process, there is no accurate way to know “how many fish I can have in my pond”.


    Correct Calculations
    for “How many fish can I have in my pond?”

  • SSA = Milligrams of Ammonia Processed ÷ Ammonia Produced by the Fish Size and Weight
  • Ammonia Produced by the Fish = Total Weight of Fish that Produced it
  • Total Weight of Fish ÷ Total Fish Size and Weight
  • Total Fish Size and Weight = “How Many Fish Can I Have in my Pond?”


  • How many fish can I have in my pond? Ahi Hydro Vortex can process 677 mg Ammonia

    Bio-filter Example: The Ahi Hydro Vortex™ filter has 677 square feet of Specific Surface Area (SSA) and is rated for up to 1,000 gallons of water. The Ahi with its 677 SSA can metabolize 677 milligrams of ammonia per day.

    677 milligrams of ammonia is produce by 3,385 grams of fish weight. (677 SSA X 5 = 3,385 grams)

    To calculate “How many fish can I have in my pond?” you can either divide the fish weight of 3,385 by the weight and size of fish, or divide 677 milligrams of ammonia by the weight and size of fish that produced it.

    From the chart below we know that an Ahi Hydro Vortex™ filter, rated for a 1,000 gallon pond, can support
    57 6″ fish (677 ÷ 11.85 = 57.13) or (3,385 ÷ 59.25 = 57.13) or
    12 10″ fish (677 ÷ 54.99 = 12.31) or (3,385 ÷ 274.99 = 12.30) or
    3 16″ fish (677 ÷ 225.21 = 3) or (3,385 ÷ 1,126.04 = 3) or
    any combination of fish with ammonia totals up to 677, or fish weight totaling 3,385 grams.

    If using an Ahi Hydro Vortex™ filter on a 500 gallon pond, simply divide the fish totals by two. If you’re using the filter on a 750 gallon pond, simply divide the fish totals by .75 …. and so on for any pond volume under 1,000 gallons.


    You MUST Know the SSA of Your Bio-Filter
    to Accurately Calculate:
    "How Many Fish Can I Have In My Pond?"

    Weight ÷ 5 = Ammonia Produced
    Ammonia Produced X 5 = Weight of Fish that Produced the Ammonia

    Fish Length, Weight, and the Ammonia they Produce

    Fish Length

    Weight in Grams
    Ammonia Produced in MG/24 hrs
    1"
    0.28
    0.05
    2"
    2.27
    0.45
    3"
    7.37
    1.47
    4"
    17.58
    3.52
    5"
    34.30
    6.86
    6"
    59.25
    11.85
    7"
    94.40
    18.88
    8"
    140.61
    28.12
    9"
    200.43
    40.08

    10"

    274.99

    54.99

    12"

    475.14

    95.02

    14"

    754.38

    150.88

    16"

    1,126.04

    225.21

    18"

    1,603.17

    320.63

    20"

    2,199.36

    439.87

    22"

    2,927.10

    585.42

    24"

    3,800.25

    760.05

    26"

    4,831.61

    966.32

    28"

    6,034.76

    1,206.95
    30"
    7,422.47
    1,484.49

    How Many Fish Can I Have In My Pond?

    Remember, when comparing biological filters, it is important to know the bacteria Specific Surface Area (SSA) it has. This allows you to compare “apples to apples” as the SSA is the most important part of the biological filter. The SSA enables you to calculate the total ammonia it can metabolize, and the total number of fish – by size – that the filter can support.

    If the biological filter you are looking at doesn’t provide you with basic SSA information, you should question why that manufacturer is withholding that information from you. Its your pond, and they’re your fish…..you deserve to know what that filter can support. 

    The most common problems of excessive algae, and sick fish are directly related to improperly sized biological filters – filters with low SSA numbers. Before purchasing a pond kit that includes a biological filter, or a stand-alone biological filter – make sure you know what you are getting – make sure to know the SSA.


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