Do Koi Clean Ponds?

Koi are omnivores – in their natural habitat, wild koi fish feed on worms, insects, aquatic plants, algae, and debris. Does this mean that koi fish can help to keep our backyard ponds clean by maintaining populations of algae under control?

Koi fish do eat certain species of algae and pond weeds. However, because koi are bottom feeders, they stir up a lot of sediment and debris from the pond floor while they feed. This can make the pond water look murky. Koi fish are, therefore, not the best fish species to clean a pond.

Keeping algae and plant-eating fish in a pond can make maintenance much easier. You can spend less time removing sludge and skimming the water’s surface to keep your pond’s water clear. Here, we look at how useful koi are for cleaning a pond and which other fish species can help keep your pond clean.

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Do Koi Eat Algae In Ponds?

Koi fish are omnivores, feeding on both plants and animals. Koi are also opportunistic feeders, meaning that they will eat almost anything. So, does this mean that koi fish eat pond algae?

Plants make up a substantial portion of koi fish’s diet, especially during the year’s warmer months. Koi fish in ponds will eat algae, especially green carpet and string algae. They avoid dangerous algal species, like blue-green algae.

Do Koi Fish Clean Ponds?

Algae grow in ponds due to the high levels of nutrients in the water that fish excrete. Koi pond owners constantly battle algae to keep it from taking over the pond and making the water green and murky, like pea soup.

If koi fish eat algae, does it mean they can help keep algae populations in a pond under control?

While koi fish feed on algae, they do not do a great job of keeping a pond clean. Koi are bottom feeders. While swimming around the bottom of the pond, searching for food, they stir up lots of sediment and debris. This makes the water cloudy, so the pond looks even dirtier.

Additionally, algae are not one of the koi’s favorite foods. Algae is relatively low in nutrients, containing mostly carbohydrates. If there are other, more protein-rich food sources in the pond, koi will choose to feed on them instead of algae.

The Best Fish Species That Will Keep A Pond Clean

So, if koi are not going to help keep a pond clean, what species of fish will?

Thankfully, there are several algae-eating fish that you can add to your pond to clean it. Many of these species can coexist harmoniously with koi fish.

Let’s look at the best fish that will help keep a pond clean:

Grass Carp

Grass carp

Grass carp are close relatives of koi but without bold coloration. They are voracious plant eaters, consuming up to 300% of their body weight in plant matter daily!

Not only will grass carp eat pond algae, but they will help to keep other aquatic plant species, like duckweed, under control so that they do not overwhelm the pond.

Grass carp are useful for keeping large ponds clean because they reach up to 55 pounds when they mature. This means that a big grass carp can eat hundreds of pounds of algae and plant materials daily!

Pond Loach

Pond Loache

Pond Loaches, also known as Weather or Dojo Loaches, are unique-looking fish that will thrive in a pond with koi. They will also help keep the pond clean because they feed on algae.

Pond Loaches grow to around 12 inches in length. Their bodies are long and slender, so they look a bit like eels! They are very hardy fish that can tolerate a range of water parameters and deal well with low water quality.

Common Pleco

Common pleco or Hypostomus plecostomus

The Common Pleco is renowned for its ability to control algae in ponds and aquariums. Their other common name is Suckermouth Catfish.

They suck onto the bottom and sides of a pond and scour off all the algae and small invertebrates. Plecos love eating green carpet and filamentous algae.

Plecos are territorial towards others of their kind. Individuals need at least 1000 gallons of pond space to themselves, so if you have a smaller pond, stick to keeping just one!

Siamese Algae Eater

Siamese Algae Eater

The Siamese Algae Eater is also a carp, so it is closely related to koi. Large fish reach half a foot in length, so they do well in bigger ponds.

As their name suggests, these fish love feeding on all kinds of algae. They have a ravenous appetite! Siamese Algae Eaters are not fussy and will even feed on types of algae that other fish avoid, like red algae and pond scum.

Siamese Algae Eaters are excellent fish for cleaning a pond and can live peacefully amongst koi. The only disadvantage is that they don’t cope well with temperatures below 70°F.

Mosquito Fish

Mosquito Fish

One of the most annoying things about having a backyard pond is the mosquitos! During spring and summer, you are sure to see their squiggly little larvae swimming in your koi pond.

Unfortunately, koi fish do not have much appetite for mosquito larvae. However, Mosquito Fish (Gambusia) are voracious eaters of mozzie larvae.

Mosquito Fish are tiny – about the size of a guppy. You need one Mosquito Fish per square foot of pond surface area. This stocking rate will keep your pond free from mosquitos!


Koi fish are not very good at cleaning ponds because they are bottom feeders. While they do feed on algae and debris that build up in a pond, they also stir up a lot of sediment and sludge while they feed. This can make the pond water murky and dirty looking.

You can keep other fish species with koi that will help keep the pond clean. Siamese Algae Eaters, Pond Loaches, Common Plecos, Grass Carp, and Mosquito Fish are excellent candidates.


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