top of page

Koi Care Primer

Koi fish swimming

Maggie here, with another post for our water-loving readers. Many pond owners want to add living flowers to their water garden; living flowers in the form of beautiful koi fish. So I thought a koi care primer was in order.

Some Koi Care Facts

  • Koi are just carp that have been selectively bred to produce those bright, vivid colors.

  • The word "Koi" means romantic love in Japanese.

  • Koi go into a state of torpor when the water is cold. They float just above the bottom, all bodily functions slowed down, barely moving at all, and living from their fat stores. Koi cannot digest food well during torpor. As the water warms in the spring, they become more active and begin feeding again.

  • Koi spawn when all the elements are in perfect synch, including water temperature. Here in Central New York, the last week of May to first days of June are primetime. Spawning only lasts a few days and the experts say it only happens once a year. I’ve had them spawn three times in one summer. So much for experts.

  • To spawn, males try to crowd the female up against the shoreline or rocks, to help her squeeze out her eggs. He then swims over the eggs and fertilizes them. Sometimes two males will squeeze a female in between them. They chase the females around relentlessly, but usually in spurts. It goes on for an hour, then they’re calm for a few hours, and then they get all wound up again. It’s over in a couple of days.

  • Koi “fry” (babies) are itty bitty. Here’s a photo of some newly hatched koi fry. Those straight black lines in the water near them are pine tree needles, that's how tiny those fish are!

Baby Koi fish aka Fry

How to Feed Your Koi

You're going to need a submersible thermometer. Suspend it at a little more than half your pond's depth.

  • When the water temperature is below 50º Fahrenheit, do not feed your fish at all.

  • When the water temperature is 50-60º F, feed a wheat-based food, sometimes called "cold weather" koi food.

  • When the water temperature reaches 60º you can switch to their regular koi food.

Choose a quality food that your fish enjoy. Look at the ingredients and use your judgement. *Foods with synthetic color-enhancers can be bad for your fish.* Any color-enhancement in fish food should come from naturally colorful food sources, not from chemicals.

Do not overfeed. There should be no food left on the pond's surface after 5 minutes. If there is, you're overfeeding. And the reason not to overfeed isn't because your fish will get plump. It's because it will devastate your water quality.

Speaking of which...

Water Quality

Get a water test kit.

(We don't yet sell these ourselves; this is our Amazon affiliate link.)

Pond Master Test Kit

Once you have your kit, get accustomed to using it. With small ponds, new pond owners should start out testing frequently, and if things are way out of whack when you do that, test more often. If things are always the same, test less often. After you've had your pond for a while and the pond is established, you won't need to fuss with this testing unless you notice something is wrong. Especially if it's an Aquascape pond like the ones we install. These ponds are complete ecosystems and should stay very stable once established.

The more fish you have, the worse and less stable your water quality will be. Koi need more space than you think. Your little 6-inch fish can grow to 30 inches over the next five years. These are long-term members of your family. They need space and care to thrive. Too many fish in a pond is like too many astronauts in spaceship. Limited resources can only support so much life.

Here's a chart for estimating the number of fish your pond can sustain.


250-300 Gallons

1-2 Koi

500 Gallons

​3-4 Koi

750 Gallons

4-5 Koi

​1000 Gallons

5-6 Koi

1250 Gallons

6-7 Koi

1500 Gallons

7-8 Koi

1750 Gallons


2000 Gallons


As you can see, this is based on a formula of about 250 gallons of water per fish, so you can extrapolate for larger ponds. An expert I know once told me her formula was 200 gallons of water per fish. I think more is always better. They should be happy and comfortable. Fish are sentient creatures, and your pond is their home.

If you don't know how many gallons of water your pond holds, here's a calculator.

More koi fish
Living Flowers

Fish in Winter

A pond depth of 3 feet is enough for Central New York koi to survive the winter. The only requirement is that the water doesn't freeze down to the lowest depths, and that there's enough room below the frozen water for the fish to float freely.

There must always an opening in the surface to allow toxic gasses to escape. The pond must never freeze all the way across the surface. Always keep a hole open in the ice.

If you have moving water such as a stream or waterfall spilling into your pond, that will keep an opening and aerate the water all winter long. If you shut your waterfall off by winter, your fish will die, so you'll have to put in a small aerator to keep the surface open.


If you have fish, you will have predators. The Great Blue Heron is hungry for fish, as is the squatty little green heron, who skulks around the shore like Groucho Marx, only instead of cigar, that's one of my fish in his beak. &*(^*%^&^)**^%!

Ahem. Sorry.

We have bald eagles who hunt nearby now. I saw one eyeing the pond once, but I've never seen one hunt there, nor the (similar) osprey who pass through on their migration routes in spring and fall. But ohhhh, those king fishers! They spot our fish, and then proceed to call in all their friends before the leader squawks, "Dive! Dive! Dive!" and do they ever!

L to R top: Great Blue Heron, King Fisher, Bald Eagle, Green Heron. Row 2: Black Bear, Mink, Raccoon, Fisher

But that's the just the air-based gang. On the ground we have pine martens, fisher "cats," minks, raccoons, and even black bears in our area, all well-known fish-lovers. So our babies can get attacked from above and below.

Our pond is a big old mud-bottomed farm pond that's soon to have a makeover. (We'll do a series of posts on that project once we get started!) So our fish have room to hide. That did not stop us from trying every possible method to keep predators at bay.

  • We bought heron decoys, moved them daily, even hung feathers from them to make them more realistic.

  • We bought reflectors and big yellow beach balls that were supposed to replicate a hawk's eye.

  • We had actual hawks doing daily fly-bys. (We didn't book this, they just showed up.)

  • We had spinners and reflectors of all kinds.

  • We had me, Mrs. Pond Guy, running outside waving my arms and shouting like a maniac whenever I saw anyone stalking my fish.

The One Thing That Worked

Yes, it was a 20-foot, whacky waving-arm inflatable tube man. It worked beautifully for two seasons. No fish-eaters wanted any part of it. But then we left it out in the rain one too many times or something, and the motor died.

We haven't replaced it. It never really fit the serenity of a koi pond in the first place. But if you are determined to keep predators away, save money and go directly to the tube man. None of the other things we tried worked at all. Not even a little bit.

I saw a video where the pond owner had built motion-detecting water turrets, that would turn and spray his pesky blue heron the minute it landed, but it didn't stop the bird. He just kept coming back until he found a way to duck under the water blasts like a contestant on one of those Japanese obstacle course shows. He got the fish anyway.

Make Peace.

It's Nature.

I don't run out screaming anymore. I open the window and have a reasonable conversation with them, and the offending birds will generally fly away. Sometimes they make me walk all the way out there before they'll leave, and that's okay with me.

So far, our earthbound predators have mostly stayed away. We did find a few headless goldfish out there one morning this spring. I have no idea what animal eats just the heads of small fish. Maybe a turtle was snapping at them and some of the bodies floated free. Who knows?

I'm trying to be at peace with nature and it seems the less I fight against it, the fewer predators I see. Three's a deeper lesson there, but that's for another blog. :)

A Whole New World

Having a pond, especially one with beautiful koi fish, expands your home and your world. You'll build long term relationships with your fish. They are individuals with unique personalities of their own. They can even be playful! You'll soon become a font of knowledge about your new friends, all your new plants, all the other wildlife who will enjoy your water, and all about about pond care.

A backyard water feature makes life better in every way. Your days become more peaceful, more beautiful, more tranquil, more restful. It's transforms home into that beautiful resort where you wish you always wish could stay longer.

It's paradise in your back yard!


Have pond or water feature-related questions?

Let us know and we'll try to answer them in a future blog post!

14 views0 comments

Recent Posts

See All


bottom of page