How many fish can fit in your Pond?

If you are building a new pond or have a pond you want to spruce up, adding fish might be on your list of things to do this season. Knowing how many fish can be supported in your pond can be confusing, so we’ve put together a few guidelines to help you make an informed decision. 
A few key factors determine the number of fish that can live comfortably in an outdoor pond such as the size of the pond (surface area and volume), the type of fish, the filtration system, and the aquatic plants or decorations in the pond. Some fish require more space than others. Koi, for example, need more room than goldfish. 

The surface area of the pond is important because the surface is where the oxygen transfer happens, so a deep pond with a small surface area can hold less fish than one with the same volume that has more balanced proportions. The pond’s volume is also a factor because a pond that is too shallow can restrict the movement of fish. Koi should not be kept in a pond that is less than 3 feet (1 meter) deep. 

There are a few rules of thumb that you can follow to determine how many fish can be put in a pond. Estimates resulting from both methods apply to larger varieties of outdoor pond fish only (measuring more than 12 inches long). The smaller the fish, the less water it requires per inch of length. Consult your fish dealer for advice on specific pond fish species. 

  • Allot at least 35 gallons of pond water per inch of Koi and at least 20 gallons of pond water per inch of goldfish. A pond with 200-3,000 or more gallons of water is suitable to hold fish. A pond under 200 gallons of water is not ideal for fishkeeping. To estimate the volume of your pond, use the formulas below. 
  • For circular ponds, measure in feet the Diameter x Diameter x Depth x 5.9 = Total Gallons  
  • For rectangular ponds, measure in feet the Length x Width x Depth x 7.5 = Total Gallons 
  • Allot at least 1 square foot of surface area per inch of goldfish and at least 10 square feet of surface area per Koi fish. To estimate the surface area of your pond, multiply the longest width by the longest length of the water feature. For example: A 5-foot by 10-foot pond is approximately 50 square feet of surface area, which means up to 25-50 inches of goldfish can be supported. 

We understand that stocking your pond with fish can feel irresistible but try not to get carried away and overstock your pond. An overstocked fishpond will experience high amounts of ammonia that spike in the heat of summer. This can cause an unfortunate loss of fish overnight. Fish need room to swim, grow and reproduce. Start with a small amount (approximately 3 or 4 fish) to make sure the ecosystem and filter are biologically ready to support a larger amount of aquatic life. For new pond owners, add a few fish over a 30-day period to ensure survival. If you find yourself with too many pond fish, use a resource like Don’t Let It Loose to locate new homes for them.  

Want to increase your pond’s fish capacity? Enhanced filtration, select water treatments, and aeration can help.  

  • Enhanced filtration can mean something different to each pond owner. Whether it involves upgrading your pond filter, adding an additional filter to your system, or adding a UV Clarifier, always start here. Enhanced filtration increases the number of fish you can keep because it ensures their waste is eliminated from the water promptly. 
  • Using select water treatments routinely like Pond Cleaner Tablets or the power-duo Water Clarifier and Sludge Remover can control odors and keep the water clean, clear, and healthy for aquatic life by breaking down fish waste, phosphates, nitrates and other pollutants.  
  • Aerating water features are another way to increase the fish capacity because the feature uses bubbles and splashing water to introduce additional oxygen into the pond ecosystem. More oxygen is always best in a fishy environment. 
  • Bonus: Did you know that some aquatic plants are natural biological filters? Consider adding pond plants for a water quality boost. 

Despite these beneficial options, fish still need a certain amount of space. When in doubt, contact your pond fish dealer. 

Alright, TotalPonders. It's time to get out your notepad and calculate the size of your pond, research the needs of the fish species you want, and get to stocking your garden pond! Remember that fish grow over time, so plan for their full adult size.