How many fish can your pond hold?

No one likes to be crowded – and fish are no exception. An overstocked pond can make your fish unhappy and unhealthy. Parasites can spread and bummed out fish tend to have diminished color. Not enough space and oxygen can even be fatal.

Be smart when you stock your pond. Here’s what you need to know.

Do the fish math

First, consider your pond’s water capacity. If you don’t know it, some quick math can give you a ballpark idea. Take measurements in feet. Then use the right equation to figure out hoe many gallons of water your pond holds:

  • If your pond is rectangular-ish, multiply length x width x average water depth x 7.48.
  • If your pond is round-ish, multiply diameter x itself x average water depth x 5.9.

Be sure to measure from the inside of the rocks and keep your measurements in feet.

For example, if a pond is 12’ x 15’ with an average depth of 15”, we would calculate 12 x 15 (= 180 sq. ft) x 1.25 (15 inches has to be converted to feet – 15/12 = 1.25) x 7.48 = 1,683 gallons of water.

Once you know the number of gallons in your pond, you can start thinking about the types of fish.

Different fish have different needs

The general rule used to be one inch of fish for every gallon of water. That’s a fine rule if you’re talking about 10 tiny fish in a 10-gallon aquarium. But it doesn’t hold water if you’re talking about two 10-inch fish in a 20-gallon aquarium. Those are going to be some crowded fish.

Good Earth Water Gardens works with many homeowners who keep koi in their ponds. For koi, we generally recommend 50 gallons of water for each inch of fish. For folks who keep goldfish, the rule is 40 gallons per inch of fish.

On the surface, this is pretty easy to figure out. But fish grow. And reproduce. And that can make maintaining a spacious aquatic home tricky.

Dealing with fish growth

Consider how big your fish will be at maturity. For domestic koi, that can be in the neighborhood of 12 to 15 inches. Japanese koi can grow up to 26 inches. When you’re first introducing fish to your pond, plan for these sizes. Your fish will be grown before you know it. Female koi tend to be much bigger than their male counterparts. And when male and female fish love each other very much, you can end up with baby fish. Be prepared to move some fish if you have a population explosion.

Maintaining water quality

More fish can mean more gunk in your pond. Algae can start to take over, filters need to be cleaned more often, and oxygen levels in the water can drop.

Like having fewer people making a mess in your house, fewer fish can mean a cleaner pond. But if you’re running into algae and gunk, you can improve the situation with a larger filter or larger pump. Bubblers or a waterfall can keep water moving, adding more oxygen to the water and alleviating the stagnant water that’s algae’s best friend.

Worst case scenario, you may need to remove some fish from an overcrowded pond. And finding homes for fish can be more difficult than it should be. Luckily for homeowners in the Kansas City metro, our local water garden society has a fish rescue program if your pond ever becomes too crowded. However, it’s best to plan ahead and manage your fish population from the start.

Good Earth Water Gardens can help you create, maintain, or revamp your pond. Whether you’re interested in getting fish or are a seasoned koi owner, we can ensure you’re providing a healthy environment for your aquatic friends. Give us a call at 816-749-8090 – we’re happy to help.