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. emme April 8, 2018 at 8:06 pm

    My dad replied:

    “True story : The fish has been covered with the green algae on the dorsal fin a few months. I was trying to catch the fish a long tome ago but it was so hard to catch it. Last a few days ago, the fish started coming up looking for food and swimming very fast. A very healthy fish no sign of any illness apart from the green algae on the dorsal fin. I happened to be just lucky to catch it up with a net when it came approaching me for food. The fin was already eroding . The green algae were rubbed off with brush soaked with salt paste. I think it was too a big shock for the fish to bear when I held it without first putting it to sleep. Very stressful it could be ! Imagine when a guy was having operation without anaesthesia! Secondly, the water was still cold so the chill and stress further suppressed the immune system. Although the day when I put the fish back it stilled looked ok, but the next 1 to 2 days after, it never recovered . I should probably treated the fish when it is warmer.”

    • Venus April 9, 2018 at 7:55 am

      It’s entirely possible. I have just recently instructed oral digestive health remedy as a preventative treatment on a fish that was exhibiting good health, and it died soon after. It’s tank mate was having floating issues, and was treated successfully. It was quite a shock for everyone involved. The fish was blind, and 13 to 14 yrs old. I’ll be writing an article on the topic soon, however, a healthy fish is easily able to endure being handled. The fish was obviously in poor health. It doesn’t take much to push a sick fish over the edge, and shock is just one way of pushing. In some cases, the fish has to be handled; it’s catch 22 I guess

      My thought is, the fish I recommended treating wouldn’t have lived much longer, and the same is probably true for your fish, so don’t go beating yourself up. Let’s both just learn from the experience. In the future, I won’t recommend handling a old fish unless it’s life depends on it; lesson learned

  2. Venus April 2, 2018 at 5:55 am

    From what I’ve learned, the green is a form of bacterial infection, something similar to, if not impetigo. Some say it spreads to other fish, but in these cases the water is unhealthy. This is a rare condition. I’ve seen two other cases, each located on the body, and no real sign of infection; just the green coloration. In both cases, the fish were just fine. It would be interesting to know if the green was short term, but that was a while back

    Clamped fins indicate either ammonia poisoning or high KH levels as you know, but I just wonder if the fin wasn’t clamped, but limp. The dorsal fin collapses when a fish is really sick. Healthy fish have erect fins, although you’ll see the fin move up and down as the fish swims about. It might be hard to tell with a Koi; most having short fins, whereas goldfish have larger dorsal fins, making it more obvious. There are breeds of goldfish with no dorsal fins; very strange

    I’m not sure I would recommend rubbing salt directly onto a wound of a fish. It’s possible the infection entered the blood stream, killing the fish, but it’s also possible the fish died from salt poisoning. If infection could enter the blood stream via a wound, so could the salt. A salt bath would have been just as effective, and safe. Freshwater fish have a very strange reaction to salt. The salt dip; more extreme than a bath, if done properly, causes the fish to pass out. Once the fish is placed in freshwater, it revives instantly. It has to do with the chloride in salt, and is probably related only to the salt coming into contact with the gills. A dip isn’t long enough to allow much salt to enter the blood stream

    No matter; just theorizing really. We’ll never know the direct cause. Another member just lost a fish after treating with my Digestive Health therapy. One fish was floating due to being constipated, so we treated that fish, and it improved asap. The second fish was treated as a preventative measure, and it died soon after treatment. It thrashed around, and went into a panic. Both fish are 13 to 14 yrs old. I would think the fish died of a heartache, so you see? You never know. Maybe the fish died of something completely different than what is obvious

    Young people can have strokes and heartaches, and so can young fish. In the future, I won’t recommend handling an older fish unless it’s necessary. Goldfish and Koi are prey fish, and they go into shock easily; stress can kill. I feel another article coming on

    Strange reaction to salt. I would say the fin was eaten up by the bad bacteria, and the tissue was pretty much destroyed before your dad rubbed the salt on.

    It doesn’t surprise me; the loss of a few fish this winter. The fish were in rough shape, even though we started buffering the water before winter hit, they didn’t have enough time to regain good health. Winter is hard on fish, but this isn’t necessarily a bad thing. Having a large pond with a large school is very different than having a few fish in an aquarium. It’s not easy to spot something off until it’s too late

    I’ve always thought of winter as Mother Nature’s way of culling the weaker fish from the school. The end result is a healthier school

    We’re almost done with Old man winter, so hang in there. Once the water has warmed, look the fish over, and see if any others are looking poorly. It’s not practical to treat the entire pond with a remedy, but we could bathe the fish in a remedy. Hopefully, it won’t be necessary

  3. emme April 2, 2018 at 12:54 am

    Hi Venus,

    The outdoor temperature is still 4-11 degrees celcius. We have odd days thats are 14-15 degrees but they quickly drop back to colder temperatures so we still have not fed the koi.
    Currently ammonia/nitrite/nitrate=0, KH=100, GH=100, pH=8.2.
    We have lost a few koi this winter. The most recent one occured a few days ago. The dorsal fin had a strange green growth on it. My dad rubbed salt paste (aquarium salt+pond water) on to the dorsal fin but a few days later, that fish died, with fins clamped and dorsal fin shredded/gone. Do you think it was a bacterial infection?

  4. 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

  5. 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?

  6. 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

  7. 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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