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


About the Author:

Profile photo of emme


  1. Profile photo of Venus
    Venus July 22, 2017 at 6:34 am

    We’re getting there. If KH is still at 80 or higher after next test, we can add the garlic remedy. Keep in mind, your pond is huge, and you’re adding a lot of water to keep the table high, and the parameters were really low to start with

    Keep it up

    Your pH reading is right on target according to KH

  2. Profile photo of emme
    emme July 21, 2017 at 11:45 pm

    Hi Venus,

    Ive been doing 2 pounds Epsom 16-32oz soda and it’s had little effect.

    Yesterday night I added 4pounds of Epsom and 48oz of soda and it finally moved the KH and GH.
    Tonight KH was 80 and GH was 100. pH was 7.8-8.
    I proceeded to add another 2 pounds of Epsom and 16oz soda tonight. Yes, mixed in warm water.
    Will see what the readings are tomorrow night!

  3. Profile photo of Venus
    Venus July 21, 2017 at 6:34 am

    Those parameters just aren’t budging are they. Are you dissolving the soda in warm wat

  4. Profile photo of emme
    emme July 21, 2017 at 12:35 am

    Hi Venus,

    KH was 30 and GH was 60 today.
    I added 4 pounds of Epsom and 48oz baking soda. Will retest tomorrow.

    Haven’t had a chance to look at filter with parents yet. Will soon

  5. Profile photo of Venus
    Venus July 20, 2017 at 12:10 pm

    You got it. I should have thought of it before, but I rarely recommend them, and then only for aquariums due to the size

    If you take the filter apart and feel in another world; take a pic or two, and maybe I can advise

  6. Profile photo of emme
    emme July 20, 2017 at 11:37 am

    I like the idea of the shells. So I would remove the carbon/charcoal (if that is what is in the filter) and replace with 10 of these shells?

  7. Profile photo of Venus
    Venus July 20, 2017 at 9:59 am

    You may have a filtering system that’s holding on to the soda; check it out. It may be necessary to change it up. I was thinking, most filters collect stuff, but if your filter has carbon or charcoal, let’s replace it with wonder shells

    Wonder shells designed to increase KH and GH; brilliant really. Once the levels are right, the shells stop breaking down. Thing is; very pricy for a pond your size. I did a little searching, hoping to find shells for giant ponds, but this is the largest I could find. Also researched mineral blocks for horses, and no, they won’t work. One good thing about using the wonder shells, much less labor for your parents

Leave A Comment

View My Stats