2 Ways To Figure Out How Many Fish Per Gallon Will Fit In Your Pond

Brad decides it’s finally time to add some fish to his koi pond.

He hasn’t already added any because he wanted to get used to having a pond in his backyard first. It still amazes him every time he looks outside. But now that he mostly knows what to expect he wants a little more.

That ‘little more’ are koi fish. He’s been doing research on taking care of them, including finding this gem on pond fish questions and answers.

But he doesn’t know how many to get.

Beautiful koi fish

Are there a certain number? What happens if there are too many? How can he find out how many fish per gallon will fit in his pond? His research leads him to these answers and more. Here is what he finds.

Pond fish come in many different types >>

What To Consider Before Adding Fish To Your Pond

Think about the type of fish. How large can they grow, how often do they breed, and how many lil fishies they can have. Depending on these answers, you may have to get better filters and pumps. Flow rate, temperature, and even climate can also affect how many fish you can have.

Now let’s look at the fish per gallon method for measuring how many fish can fit in a pond.

Method 1 – Inches Of Fish Per Gallon

For this method, you’ll need to find out about how many gallons your pond holds. One option for finding it is contacting the contractor who built it. They may still have the numbers. If not, someone will be doing a gallon calculation:

Square/Rectangular Ponds: Length x Width x Average Water Depth (feet) x 7.5= gallons
Round ponds: Diameter x Diameter x Average Water Depth (feet) x 5.9= gallons

You will also want to know the type of fish you’ll want. Many species require different gallons per inch. Here we will cover koi and goldfish per gallon.

A standard rule for how many fish per gallon in a pond is 35 gallons minimum per inch of koi and 20 gallons per inch of goldfish. For example, Jess has a 10’x15’ pond that is an average of 2’ deep (the minimum depth for having fish). Her gallons capacity is 10’ x 15’ x 2’ x 7.5= 2,250 gallons. 2,250/35 gallons for koi means she can have 64 feet of koi (or about 771 inches).

You may not want to put in the maximum number as koi grow over time.

Speaking of maximum, what do you think happens when a pond has too many fish?

What Happens When You Over Stock Your Pond With Fish?

Your fish can become sick or get parasites.

Your pond can become a breeding ground for parasites and bacteria. A lot of fish means a lot of waste. This puts pressure on the pond filters. If they can’t keep up then it’s just recycling dirty water.

This leads to more algae forming, and quickly too. Then your pond looks nasty.

Too many fish also raises the ammonia levels in the water. This is dangerous during the summer. Ammonia levels rise in the summer heat. Add that to the higher levels with too many fish and they can die overnight.

Too many fish per gallon in a pond

Would you be happy living in a room with too many people?

Your fish aren’t. Too many of them can make them uncomfortable and unhappy. This can cause their colors to become less vibrant and they can lose their appetite.

You can also suffer from having too many fish in your pond. Your pond will need more maintenance on your part, which means it can become more of a chore than anything.

If gallons isn’t for you, try out our next measurement for how many fish will fit in a pond.

Method 2 – Square Footage Of Surface Area Per Inch Of Fish

First, you’ll want to measure the total square footage of your pond:

Square/Rectangular: longest Length x Width
Round: radius x radius x 3.14 (radius is half the pond length)

For how many fish per gallon in a pond, keep in mind it’s best to have 10 square feet for 1 koi. For other fish, it is 1 square foot of surface area per inch of fish. This means Jess’ 10’x15’ pond has 150’ of surface area (10′ x 15’= 150′). That shows us she can have 15 koi fish in her pond maximum.

Well, unless she changes her pond so it can support more fish.

3 Ways To Make Your Pond More Comfortable For Your Fish

Add in less fish.

Your fish will more than likely breed, making tiny little fishies. It’s basically like having free fish! Their numbers will grow, it just takes some time.

If you aren’t sure how many fish to add, do so gradually. Adding in a few over a 30-day period can give you a good number. It can also prevent you from having extra fish that you need to find a different home for.

How many fish per gallon is important for their health and comfort

You can also add in more aeration. Aeration adds oxygen into the water, making it possible for fish to breathe. More oxygen for more fish.

Upgrading your filters and pumps can also make the pond more comfortable. Water conditions will improve and your fish will be happy and healthy.

Fit In Your Fish (Comfortably)

Right now, Brad is doing what you can soon be doing: enjoying his new pond fish. He can see their scales flash in the sunlight as they either lazily float or dart through the water. The best part is being able to feed them!

Feed your fish the right way >>