Sick Koi

Sick Koi

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 13, 2018 at 6:55 am

    Hi Emme, I was just thinking about you, and wondering how things were going

    In most cases when a fish tilts to the side, it’s losing consciousness. Winter is a tough time for fish, and even though your fish experienced health issues previously, they had a few months in healthy water before winter set in, which gives them a fighting chance to survive the cold. In their natural habitat, they would experience the same cold water, becoming dormant. Only the strong survive. This is the way it is in the wild, and the not so wild as well. There’s a chance you could lose a fish or two over the winter, but there’s a better chance they’ll all survive

    If the fish has a health issue, the cold water will benefit. Goldfish and Koi alike use less oxygen in cold water, so most health issues are put on hold until the water warms. This is when will see any unresolved issues crop up

    Are any of the pumps still running?

    You have algae, so if any of the fish are hungry, which is doubtful, they can indulge. Lack of food can cause the swim bladder to collapse, which causes the fish to lose the ability to lift or swim, so that’s not the case here

    As long as the bottom of the pond isn’t freezing over, we’re good. I wonder if your Dad is seeing the same fish, or different fish? or more than one at a time?

    Is most of the surface frozen? all or none?

  2. emme January 13, 2018 at 2:41 am

    Hi Venus,

    The koi pond has been dormant for several months now. Outdoor temperatures are always below 10degrees C (range from 3-8). We haven’t fed the koi since the beginning of Winter. I’ve still been checking the water chemistry every few weeks. The fish are generally camping at the bottom of the pond. Recently, my dad has noticed that one of the medium size koi has been lying on its side (gills up) instead of vertically (dorsal fin up). When he went to take a closer look, it swam away. He says he’s seen other koi lie like this during dormancy in the past. Why does this happen? Is the koi too tired? Malnourished/lack oxygen??

  3. Venus November 12, 2017 at 8:21 pm

    If the fish aren’t feeding at all, one pump should be sufficient, but if the weather warms for more than a few days, and the fish show interest in eating, I would plug in another pump. The warmer the water the more action you need. The colder the water the less action needed

    The parameters look great

    I know it’s nerve wracking; dormant fish, but nature is taking her course. Fish that experience dormancy in the winter live more years than fish that don’t

  4. emme November 12, 2017 at 7:12 pm

    Hi Venus,

    The comments box seems to be working well again.

    Tested water today with these readings:
    Ammonia/nitrite~0. Nitrate 5-10. pH=8.2-8.4, KH=110-120, GH=200.

    Outdoor temperatures have been around 10degreesC. We usually just go with the air temperature because we don’t have a pond thermometer.

    The fish seem to be dormant as before as they don’t swim around much and float on either end of the pond. Do you think we should leave 2 pumps unplugged at 10degrees or just 1?

  5. Venus November 7, 2017 at 5:14 am

    Thanks Thuner. All is well

  6. thunder174 November 7, 2017 at 1:55 am

    finaly got in lol at least mine working hope her fishie gets better

  7. Venus November 4, 2017 at 5:45 pm

    Testing comments

  8. Venus November 3, 2017 at 6:31 am

    It’s normal for some fish to reach a state of dormancy faster or slower than others. It’s possible the water is warmer under the waterfall. They’re not too cold though. Your fish can tolerate temperatures above freezing, so your fish are okay. If fish are swimming around, and show interest when you walk up to them, feel free to feed them food high in roughage, but small amounts

    It is a tricky time, but the fish have the answers. If they’re eating, the friendly bugs are eating too. Trouble comes when the friendly bugs aren’t eating, and food is being added to the environment. The food turns to waste as soon as the weather warms, and then the friendly bugs are unable to convert the large amount of waste. If the friendly bugs aren’t dormant, and no food is being fed, they starve and die out, causing a spike as the weather warms. Did that all make sense?

    If a spike happens, you’re ready. You understand the cycle, and are prepared with water treatment

    Ammonia is created from the waste your fish produce, and ammonia is the first toxin to form in the cycle. Some fish keepers look at it as a bad thing, but it’s the food source for friendly bugs, and without it, there would be no life in our natural bodies of water

    You’re not seeing nitrates, the end result of the cycle, because your fish aren’t producing waste. As long as the friendly bugs are dormant, they don’t require food, so I think everything is going well. Time will tell

  9. emme November 3, 2017 at 12:20 am

    Hi Venus,

    It was 3 degrees C out today and the temperature may drop to negative 2 C in a few days. We noticed many of the larger fish seem to be hanging out near the base of the pond under the waterfall. Dormant? Or just kind of floating at the bottom with little movement. We unplugged 2 pumps closer to the waterfall. Some fish are still swimming around.. not sure why. Dad has stopped feeding for almost a month since the outdoor temperatures dropped below 10C. Today ammonia,Nitrite,Nitrate were pretty close to 0 (lowest color on scale). KH was 120 and GH was 220. Hopefully everything will be okay…

  10. Venus November 2, 2017 at 4:39 pm

    No, don’t cover the surface for any reason. If the surface freezes over; all or some, the water will be cold enough that the fish are completely dormant, and won’t need any oxygen. This is the only cover your pond should ever have

    As for the second pump; remember the trouble you’ve had with the water. Moving water is healthy water. I think they would be safe in unplugging the second pump if temps reach just above freezing; say 4.4 ish. Your fish won’t reach full dormancy until then. You may still be feeding at temps of 10 c or 50f. Food makes waste which makes Co2 which reduces oxygen. You’re safe to turn off the pumps if you and the fish aren’t feeding

    If you have any exposed pump cords, best to insulate them; keeps the cords from cracking

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