If you are building a new pond or have a current pond you want to spruce up, then adding fish might be on your list of things to do. Knowing how many fish to add can be confusing but here are a few ways to calculate the perfect amount to add to your pond.
Try not to get carried away and overstock your pond with fish. Too many fish can overload the pond with high amounts of ammonia that spike in the heat of summer causing an overnight loss of your fish. They need room to swim and grow and may even reproduce. Start small with 3-4 fish, especially with new ponds, 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. You also don’t want the problem of having to sell or get rid of extra fish.
Many factors determine the number of fish that can live comfortably in an outdoor pond like the size of the fish, species, and size of the pond. Also consider the total surface area, volume, size and type of filtration system, the flow rate, temperature, and climate. Surface is very important because the surface is where oxygen transfer happens, so a deep pond with a small surface area will be able to hold less fish than a pond with the same volume which has more balanced proportions. However, volume is also a factor because a pond that is too shallow can restrict movement of the fish. Koi should not be kept in a pond that is less than 1m deep.
Good filtration and water features could allow you to increase the capacity of fish. Having more filtration will increase the number of fish you can keep because it will make the water cleaner as waste will be eliminated more promptly. Also using products like pond cleaner tablets and water clarifier solution will help keep the water clean, crystal clear, and promotes a healthy aquatic environment by breaking down fish waste, phosphates, nitrates and other pollutants. Water features will also help increase the number of fish because the feature uses bubbles and splashing water for aeration that introduces oxygen into the pond ecosystem. However, fish still need a certain amount of space no matter the cleanliness and oxygenation of the water.
There are a few rules of thumb that you can follow. First, is to determine inches of fish per gallon. Allot 35+ gallons per inch of koi, and at least 20 gallons per inch of goldfish. A pond with 500 to 3000 plus gallons of water is good to hold fish. Anything smaller should avoid fish keeping. The second rule of thumb is to allot 1 square foot of surface area per inch of fish and 10 square feet of surface area for 1 koi. You can be extra cautious and do 2 square feet of surface area per inch of fish as well. To determine surface area, take the measurements of the longest width and length of the pond and multiply together. So 50 square feet of surface area means 50” of fish. Estimates resulting from both methods apply only to larger varieties of outdoor pond fish, not smaller fish measuring less than 12 inches long. The smaller the fish, the less water it requires per inch of length.
Start measuring your pond and researching the different species you’d like so your pond can be fish ready in no time!