Sick Koi

Sick Koi

unnamed IMG_4931 IMG_4935 IMG_4937 IMG_4929 pond pic

Sick Koi but good water parameters in outdoor Koi Pond??


I’m currently babysitting my parents’ outdoor koi pond and will be doing so for about 2 weeks. It’s quite a large pond (10,000 gallons and spans half of our backyard). We have several large koi (length of adult forearm) and several smaller goldfish (length of adult palm) and based on the number of fish, the pond may be overstocked. The outdoor temperature in Vancouver has been quite variable this summer (16 – 32 degrees Celcius. Low-mid 20’s this week but the temperature was up to 30 degrees over the last 2 weeks). For some reason the pond is losing about 4 inches of water each day so we refill the pond with a bit of fresh water each day (like a 5% daily partial water change!). My parents have had this pond for about 5 years.

At first glace, the fish look relatively healthy (full scales/fins) but there are always a few fish in the pond that have finrot, sores on the body or strange growths. Some fish have had raised scales, pineconing and died not having released their eggs. The fish have been exposed to salt and antibiotics many times. Sometimes the treatment works, but on average about 1 fish dies each month and my parents replace them. At the moment, one very large fish currently has sores on one side, some raised scales and prefers to swim at the bottom of the pond and doesn’t seem interested in food. Another strange observation: when I fed the fish this morning, I noticed that 3 smaller fish appeared to be chewing/biting another small fish of similar size in a corner of the pond. When I threw food at them, all of them swam away. What does this mean??

Seeing that there are always ill fish, I assumed that there must be problems with the water quality. However, when I tested the water parameters of a sample of pond water today, they seemed ok:
Ammonia: 0-0.1
Nitrite: 0-0.1
Nitrate: 5-10
pH: 7.2-7.4
KH: 10
GH: 20
Phosphate: 1

I came across your site and thought that the garlic may help. My parents usually feed Hikari pellets twice a day, so over the last 2 days I have been feeding a mix of presoaked pellets and cooked peas but I think only the smaller fish were able to see the crumbled peas because the large koi swam right through the small bits.

I have attached some images of the pond. Please let me know if you have any ideas





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  1. Venus January 15, 2018 at 6:47 am

    Start feeding one light meal a day at 54f. You would feed food high in roughage, easy to digest, such as peas, blanched green leaf lettuce or fresh spinach, and feed lightly, according to the water temps, not the temps of the air. When water temps reach 64f, you could increase feedings and add normal food

    Although they can eat algae if they’re hungry, you don’t want them eating it all

    With such a large body of water, the temps will be relatively consistent, whehter they’re rising or falling

  2. emme January 14, 2018 at 6:24 pm

    Sounds good! I’ll keep maintaining the water parameters. Will keep you posted 🙂

    Btw, when Spring comes and we start feeding again, is there a way to feed properly to ease the fish/good bugs out of dormancy? Or does the cycle and everything just work again with normal feeding?

  3. Venus January 14, 2018 at 8:26 am

    No, don’t use heaters. This just confuses the course of nature, which the fish are a part of. The school will be healthier for experiencing a natural winter.

    It’s likely the fish has some issue, but if it’s alert, I don’t think it’s serious enough to keep it from surviving. My guess is, the swim bladder is doesn’t have enough gas in it to keep the fish upright; let’s hope that’s all it is. It’s tricky, the coming of winter. The fish needs to have some waste in it’s track to keep gas in the bladder. If the digestive tract slows when the tract is too full, the fish may be unable to sink, and be exposed to water that’s too cold at the surface. If the tract slows, and no waste is in the tract, the fish may not have the boyancy it needs to stay upright

    Your pond is large enough that the water will warm and chill gradually, making it easier on the fish. A lot of fish will eat in cold water temps 40f, but this doesn’t mean we should feed them. If algae is available, and they’re hungry, this is all they need

    I wouldn’t worry about the fish. If it makes it through the winter, and it probably will, we’ll see if there are any health issues that need attention. I think you’ll be amazed at the health of the fish when Spring comes. You’re doing a great job with them

  4. emme January 13, 2018 at 12:10 pm

    Hi Venus,

    There are still 3 pumps on in addition to the waterfall running. There is a bit of algae in the pond. Nothing is frozen at the moment as the temperatures are consistently above zero. (lowest = 2 or 3 Celcius). Do you think the fish are getting enough oxygen? Dad has been observing just one fish tilted this year. He mentioned he had seen this tilt from other fish during previous Winters and was wondering if it was normal. Should we just watch and wait then? Or would you recommend we use heaters?

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