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 (50,000 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




unnamed IMG_4931 IMG_4935 IMG_4937 IMG_4929 pond pic


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  1. emme August 13, 2017 at 9:37 pm

    Hi Venus,

    I haven’t’ started the new garlic treatment yet. Will soon. But I’m noticing that some fish have developed white patches on their bodies that look fungal. Just wondering if the new treatment will also cover fungus?

  2. Venus August 11, 2017 at 7:06 am

    Good deal. Things are turning around now. We lost the one fish since we started buffering, and hopefully it will be the last we lose to bad water

    Healthy fish live in healthy water

  3. emme August 10, 2017 at 11:35 pm

    Sounds good. I’ll get KH and GH in therapeutic range again and prepare for garlic recipe. I put the tub in the fridge for the time being

  4. Venus August 10, 2017 at 5:44 pm

    Start the remedy; pour it all in the quiet side, and then feed the fish. It’s to our favor there’s a quiet side of the pond for treating the fish, but once they’ve recovered, that quiet side has got to go

  5. emme August 10, 2017 at 11:28 am

    Hi Venus, we ordered 2 pumps but they will take 2 weeks to arrive. Hopefully the Wonder Shells will arrive before that.
    The mint tea and new garlic recipe has arrived. Should I hold all the recipes and maintain KH/GH until the pumps arrive?
    Or should I start mint already?

  6. Venus August 10, 2017 at 2:30 am

    If they don’t show a sponge in the ad, they don’t come with a sponge. You’ll have to buy them, and if you can’t find, you can use (black) filter sponges. You can sew them together so they slip on and off, but they do sell cylinder sponges, and they come in all sizes. I use real sea sponges. You just hollow out the inside with scissors, and the sponge slips on and off easily

    Here’s another pump even bigger for a great price; not sure if they ship to Canada though

  7. Venus August 10, 2017 at 2:26 am

    That looked to me to be a basket over the intake; where the sponge goes, not blades, but that being said, I’ve never seen a basket that looked quite like it, however, I’m sure there’s pumps I haven’t seen. It wouldn’t make since to have blades on the outside now would it

    Here’s another pump with a different shaped basket; they’re all different

    If the pump you order is wrong, you can return it if purchased on Amazon

  8. emme August 9, 2017 at 8:38 pm

    I’m not sure if these pumps come with sponges. If not, should we buy and attach our own?
    Venus, we are planning one buying one 1800gph and one 2400 gph pump from the Amazon links I sent you. Both pumps have a horizontal spindle attached to the side. Are those safe for the koi? I don’t think we have those on our current pump and I just want to double check with you since it’s quite a large purchase!

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