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 16, 2017 at 7:45 pm

    Pond draining in progress. Leak is slowing and 2 new pumps ordered as extras/add-ins if needed. The pond guy came to fix the skimmer today and stick a pump to the skimmer. He was impressed by how much better the koi looked! We sure have come a long way since the beginning and all thanks to you, Venus 😀

  2. Venus September 16, 2017 at 9:56 am

    Maybe so. The goal is to have the entire surface agitated, except for maybe a 10’x10′ area where the water fall is. This way, you have a place to feed and or treat the fish

  3. emme September 16, 2017 at 1:40 am

    Hi Venus,

    With the pond level lowering and waterfall off, I’m noticing several slower areas of the pond. Our pond is around 10,000gallons. 3x1800gph pump + 1x2400gph pump is only 7800gph. Shall we add 1 more 1800gph or 2400gph pump?

  4. Venus September 9, 2017 at 2:05 pm

    Excellent KH readings, as our pet shop testers read 20 ppm lower than what actually is. Yes, this is true. Good idea, waiting to add the additional pump, but keep in mind the water fall does little to oxygenate water. The action disturbs the surface a bit, which is good, but doesn’t eliminate Co2 from the water, however, aren’t they beautiful?

  5. emme September 9, 2017 at 11:51 am

    Hmm.. okay! I think the only way to find out would be to start draining and test KH and pH when the waterline is low enough that the waterfall does not work.
    I’ll wait for the new pump to arrive first. I’ve been keeping KH pretty high in preparation for mint/garlic. It should be close to 130-140 today.

  6. Venus September 9, 2017 at 7:37 am

    pH levels will give you the answer. If KH is at 100 ppm, pH should be 7.8 to 8. ppm. If KH is at 120 ppm, pH should be over 8. In a pond this size, test three to four different sections. My guess is, you do have enough action, and the right kind for oxygenating water. The leak shouldn’t interfere with oxygen levels

    If KH is healthy, but pH is low, this tells us the oxygen levels are low; meaning you need more action. pH levels of 8. and over are the goal. A reading of 8.6 ppm should be the maximum. The only way you can go over the max is to use too much soda or H202, and with a pond your size, this hard to do

  7. emme September 9, 2017 at 1:28 am

    LOL that’s a lot of crates in the pond!

    We will soon have 3 x 1800gph pumps and 1 x 2400gph pump. Do you think just 4 pumps is enough to oxygenate the whole 10,000gallon pond as it is being drained by the leak? The major pump from the waterfall will be off as the waterfall shuts off when the water level is low

  8. Venus September 8, 2017 at 7:29 am

    Thanks for reminding me; completely forgot about this issue. Yes, I have an idea, although I’ve never done it. Place each pump in an egg crate. I think they should fit. Tie a rope on each crate; tie at the bottom, so when you pull the crate over it won’t tip

    To get the crate back in place, you’ll need a pole with a hook at the end. In my mind I see the poles the teachers used to open or close the awnings at the top of the windows. You should be able run the pole through the holes of both sides of the crate to support it, move it to it’s original spot, and lower it. Maybe you won’t need the hook at all, but I was thinking the crate might slide as you’re putting it in place

    Genius isn’t it? LOL

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