11 Koi Fish Diseases And How To Treat Their Main Causes

The only Master Aquascape Certified Contractors in Iowa

11 Koi Fish Diseases And How To Treat Their Main Causes

Find Out How You Can Help Your Fish Friends Stay Healthy In Your Des Moines Pond

Parasites, bacteria, and fungi can attack the koi fish in your backyard pond. You can find out how to spot the koi fish diseases they cause and treat them.

The different diseases, their causes, and their cures are in the post below-

We Have To Help Them!

“Of course we do, and we will, but first we need to figure out the problem.”

Ashley looks at Tyler with worry in her eyes. Some of their koi fish have been acting weird recently and she thinks they may have a disease of some sort. “Ok. How’re we going to figure out the problem?” she asks. Tyler narrows his eyes as he thinks.

“I know!” he suddenly bursts out. “Let’s just ask Google about diseases koi fish can get and go from there.” Ashley nods her head as Tyler picks up his phone.

He searches for koi fish diseases on Google. Tyler goes through answers to other pond fish questions before he gets what he needs.

Here is what he finds-

What Can Cause Koi Fish To Become Sick

“Says here it usually has something to do with…stress?”

When people are overly stressed it’s much easier for them to get sick. The same goes for koi fish. The stress keeps them from being able to fight off the diseases. It usually has something to do with a drop in water quality, overcrowding, or contamination.

“Contamination can mean pesticide, fertilizer, or even introducing a new fish to the pond that was sick,” Tyler reads aloud.

“We did just fertilize our lawn…” Ashley whispers worriedly. “I’m sure we can fix this, whatever caused the problem,” Tyler says reassuringly.

He scrolls on to see what the different koi fish diseases are.

Common Koi Fish Diseases

Koi fish diseases are usually caused by parasites, worms, or bacteria. A fungus can also start growing on fish and it isn’t good for them. Common diseases that come from these sources are:
  1. Ich (parasites)
  2. Dropsy (bacteria)
  3. Flukes (worms)
  4. Fin Rot (bacteria)
  5. Anchor Worm (worms)
  6. Fungus
  7. Fish Lice (parasites)
  8. Trichodina (parasites)
  9. Ulcers (bacteria)
  10. Chilodonella (parasites)
  11. Costia (parasites)
“Wow, that’s a lot of diseases,” Ashley says in surprise. “True, but as long as our pond is clean, maintained, and we don’t make any rash decisions our fish will be fine,” Tyle reminds her. He scrolls down to learn how to find out if their fish have a koi fish disease.

How To Spot Sick Koi Fish

“It starts with their behavior.”

Koi fish act differently when they are sick, much like people do. They’ll stay away from the group, often hanging out near the surface or on the pond bottom. They may even stop eating.

“The eating part definitely sounds like a person,” Ashley notes. 

Your fish can also be sick if they:

  • Keep their fins close to their body
  • Gasp at the surface
  • Have discoloration
  • Look different
  • Start rubbing against objects

“If they look different?” Depending on the disease koi fish can start looking different. They might have cloudy eyes, red streaks on their fins, white spots, cottony tufts, bloating, or ragged fins.

“None of those sound good. I don’t know if any of our fish have these symptoms. We’ll need to keep an eye on them, maybe put them in a basin and take a close look,” Tyler says.

He hands the phone to Ashley so she can see what the treatments for these koi fish diseases are.

How To Treat Koi Fish Diseases

Disclaimer: we are not veterinarians and not responsible for your fish or the treatment you choose. These are general treatments that should help with symptoms, but cases and results do vary. The best action to take is to call a veterinarian. They will usually give a referral to a vet that specializes in fish if needed. I had a vet actually do surgery on one of my koi in my garage a few years ago.
Generically speaking, there are 3 main types of treatments for koi fish diseases. The treatments are a broad spectrum disease treatment, a dewormer, and physical removal.

You can usually treat parasites with a broad spectrum disease treatment and pond fish treatment. “Wait, those are the actual names of the treatments haha,” Tyler chuckles in surprise. “At least they’ll be easy to find.”

You can remove larger worms and parasites, like anchor worms and fish lice, physically. Smaller worms need a dewormer treatment.

Fungus needs an anti-fungal treatment.

You can find more specific details on https://www.pondexperts.ca/koi-disease-diagnosis-treatment/

“But what about the actual cause of these koi fish diseases? If you don’t fix that then it’ll just come right back!” Ashley points out.

Fixing The Cause Of The Sickness

There are a few ways you can try to fix whatever’s causing your pond fish to become sick. They include:

  1. Making sure the skimmers and filters are working properly
  2. A full pond cleaning
  3. Water treatments
  4. Making you have the right number of koi fish


“If we really want to know it might help to ask a pond professional to come take a look at our pond. They might be able to find out what’s causing these koi fish diseases,” Tyler suggests.

The Next Steps

“You’re right, Tyler. I think that would be for the best so we don’t possibly waste time looking but not finding an answer,” Ashley sighs sadly.

They have a pond pro come look at their pond and their fish. He gives them a few solutions which they follow. A couple weeks later and their fish are healthy and their pond is perfect again.