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. emme September 8, 2017 at 2:32 am

    Feeding less has made a huge difference to readings! Ammonia=0.1, Nitrite=0.3, Nitrate=20. Will start treating mint soon.

    By the way, do you have any ideas about our issue with maneuvering the submerged pond pumps without breaking the power cords? Our only way to pull them out of the pond or place them back into the water is by tugging the pump’s power cord because of how deep the pond is and how heavy the pump is… One of the pumps has a half dead cord, a lot like a half dead phone charging cable. It’s kinda annoying…

  2. Venus September 7, 2017 at 8:05 am

    It might take longer than you think to drain to the leaking point, but…..time will tell

  3. emme September 7, 2017 at 1:01 am

    The leak has gotten larger I think but Ive only been involved with this pond since I started blogging about it!

  4. emme September 7, 2017 at 12:59 am


    If we lay down gravel substrate, will annual vacuuming be enough? Will be get lots of debris there? I need to double check with the pond guy if he has the tools to vacuum the pond floor!

    2 new 1800gph pond pumps will arrive next week. One will be used for extra oxygen and one will be used by the pond guy to fix the filtration system for debris. (we will have 3 x 1800gph pumps and 1 x 2400 gph pump in addition to the waterfall but excluding the extra 1800gph pump for filtration).

    I’m thinking we should start allowing to leak to run its course after the new pump is setup for filtration?

    One thing I should mention is that due to how deep our pond is, we have great difficulty pulling up submersed pond pumps from the bottom of the pond. It’s already difficult getting the pump to sit upright so it can spray upwards when we dangle the pump into the pond, but having to fish it up to adjust or clean is quite challenging because the only way to place it in the pond or take it out is by pulling at the electric cable/wire. One of the pond pumps doesn’t work well and sometimes stops altogether when the cable is nudged. The cable has likely been damaged inside… any solutions to this??

  5. Venus September 6, 2017 at 3:55 pm

    You could do it now. There’s always a risk of spike with fish keeping. The key is to be prepared, and to keep a close watch on the toxins. There may be a little stress involved, but I think it would be better for the ecosystem to not be topping off so often and so much; it disturbs the balance

    The city uses disinfectants periodically as needed. There may be times when the products are faint, and you don’t get a reading, but there may be also be times when it’s present. Adding tap water straight to the pond without treating is risky

    Plus, how do you know the leak won’t get larger? Did it start off small, and seems to be getting worse?

    It may actually help stabilize the cycle

    Maybe it would be better to get all these things done before winter sets in. Muck out the pond, lay the gravel, or if you’ve laid the gravel than perhaps vacuum; see what’s lurks down under. lol

    It will be a fun project, and give you a chance to look all of the fish over

  6. emme September 6, 2017 at 2:07 pm

    Nope! Not sure when we should start allowing the water to leak out. Can we do that now that we are stabilizing the cycle and about to add mint?

  7. Venus September 6, 2017 at 12:34 pm

    That’s a tough one. Hopefully, the leak isn’t too far down, and the fish can remain at home. The only way to find out is do the deed. Have you determined how many inches of water you’re losing a day? or within a week?

  8. emme September 6, 2017 at 11:36 am

    Hi Venus,

    I didn’t do a water change, we’ve been topping off the pond with more water than usual. Although, dad did clean out the canister sponges yesterday.
    He will continue to do so… I’m not sure if they’re being converted or not as it appears we do not have enough of the bacteria that converts nitrites to nitrate so we’re still seeing quite a bit of nitrites? Will keep monitoring the parameters.

    We’re wondering when we should start letting the pond drain to assess where the leak is before winter. With the unstable cycle right now, I’ve been telling dad to put that off.
    But how long should we wait for the cycle to stabilize before assessing the leak?
    Also want to do the mint and garlic treatments… hmm…

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