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 July 20, 2017 at 12:08 am

    Hi Venus,

    Tonight KH was 30 and GH was 60. I added 32oz baking soda and 2pounds of Epsom. Was a bit conservative just in case. Will monitor again tomorrow.

    My question about the Nutrafin liquid solution test kit was because I was curious why such an expensive test kit ($100) could be so inaccurate for pH. The test strips were more accurate and closely matched the petshop readings so I was wondering if it was something in the pond water that was making the liquid test go out of whack, but for some reason the test strips were immune to it and read more accurately. All the other parameters (other than pH) tested by the liquid test kit match those of the test strips.

  2. emme July 19, 2017 at 12:15 pm

    Hi Venus,

    I will test the pond water tonight before I add anything.
    The water change was from a few days ago when I was panicking from the high KH that one evening I told you about. I don’t do water changes usually.
    The soda is being mixed into tubs of pond water before being added to the pond. The temperature outdoors is 22-26 degrees celcius.
    I called and left a message at the water department. I also emailed them but it may take some time before they get back to me.
    The Nutrafin liquid test kit includes a calcium tester, should I use that on the tap water? I’m not sure my parents would be into changing the home’s filtering system though….

  3. Venus July 19, 2017 at 6:47 am

    Let’s increase the 16 oz to 48 oz

    What is the 20 gallon water change for? This may be a misunderstanding. As long as you’re topping off water, there’s no reason to exchange water. Are you mixing soda in warm water to somewhat dissolve? It may help. You may have missed that previous post. Carbonate mineral (soda) doesn’t break down well, and adding to warm water helps a bit

    You may have also missed a previous post about contacting your water department to get KH and GH readings. If the KH in your city’s water is a lot higher than your tap, you’re on a filter. It may be possible to re-route you hose water. This would only make sense if the KH was quite a bit higher. I couldn’t find the info in a online water report. I would also like to know the calcium levels in your city water. Reason being, GH is made up of two parts magnesium (Epsom) and one part calcium. I’m wondering if it would help boost GH to add calcium to the water. If you are on a filtering system, calcium is being removed from the water as well

    Did you ask your parents if they know if they’re on a filtering system? The idea of the filter is to keep the pipes clear of deposits, but if the fish are being deprived of valuable minerals, so are your parents

  4. emme July 18, 2017 at 10:52 pm

    Just added 16oz soda and 2pounds of Epsom (this is the fourth batch altogether, including the batch I put in on that evening I did the 20 gallon water change)

  5. emme July 18, 2017 at 10:19 pm

    Petshop confirmed
    KH: 40
    GH: 75

    • emme July 18, 2017 at 10:51 pm

      Just added 16oz soda and 2pounds of Epsom (this is the fourth batch altogether, including the batch I put in on that evening I did the 20 gallon water change)

  6. emme July 18, 2017 at 9:57 pm

    Hi Venus,

    It’s been about 24hours since I last added Epsom and soda.

    I just tested
    KH = 30 with Nutrafin liquid test kit
    KH = 40 with API test strips

    GH= 60 with Nutrafin liquid test kit
    GH= 30-60 with API test strips

    Shall I add 16oz baking soda and 2 pounds of Epsom? Or wait for another test tomorrow?

  7. Venus July 18, 2017 at 9:24 pm

    It’s entirely possible the leak could fix itself in time, but I would have to know more about the construction of the pond. Is it a liner? Most are these days. Is there sand beneath the liner? In a lot of cases a hole is dug, and little to no prep work. When the hole is filled with water, the weight forces the liner onto a sharp rock, and before you know it, there’s a tear.

    I guess you could go on endlessly filling and buffering. I would definitely wait it out before draining the pond. A crack in the liner will be really hard to find. Have you ever let it go to see how low the water table gets before stopping?

    H202 begins to degrade as soon as it comes into contact with live organics, so no. If you had been using it daily then possibly. I often recommend it, but your pond is so large, it would take several gallons to make any difference

    Each pH test kit you listed varied in pH, but no matter; I’m not concerned with pH right now. Why? Because it’s not a parameter; it’s a theory. When fish keepers use it, they actually cause more damage then good. Stop worrying about pH, and focus on KH

  8. emme July 18, 2017 at 11:43 am

    Hi Venus, what are some things that could account for the inaccurately high pH readings from the liquid test? We haven’t used hydrogen peroxide but it’s quite possible my dad has. He has used many different substances in the pond in addition to antibiotics.

    Ok, good so we have confirmed the leak. If we did nothing to plug the leak and performed daily water top-ups and buffered KH and GH long-term, would that be enough?

    We are currently at 3 boxes of soda (16oz/box) and 3 boxes of Epsom (2 pounds/box). Please note that there have been multiple water top-ups and there was that evening after I put in the second box that I removed 20gallons of pond water and topped up extra water. I haven’t measured any pond parameters since I added the 3rd box of soda and epsom last night. Will find out tonight!

  9. Venus July 18, 2017 at 7:43 am

    It’s good to see the similar readings for KH, which means we’re going in the right direction

    It’s good to see salinity dropping in one respect, but in another, it indicates the pond has a leak, seeing as how salt doesn’t evaporate. If it were just evaporation causing the loss, the salinity would stay the same. We’ll keep an eye on the water loss, and discuss later, but it’s going to be hard on your parents to keep KH levels up when they’re adding so much water; very frustrating.

    In most cases where KH is as low as 40, pH is close to 7. if not a little lower, so I don’t think oxygen is going to be an issue; meaning I think we’re going to find out the pumps in place are getting the job done

    No reason to add more Prime until we see a substantial change in ammonia or nitrite

    Are we at two or three boxes of soda now? Keep it up. We have a long ways to go, and a short time to get there. Let’s go with the low KH readings, and boost levels to 120 to 140 ppm

  10. emme July 18, 2017 at 1:18 am

    Hi Venus,

    Just thought I would update you on water parameters. Before adding anything this evening, I tested the water parameters as follows:

    Electric Pond salinity tester
    Salinity: 0.08

    Nutrafin Master Test Kit (Liquid; what I’ve always been using)
    -Ammonia: 0.1
    -Nitrite: 0.3
    -Nitrate: 5-10
    -KH: 30
    -GH: 40
    -pH: 7.8-8 (high pH tester), 7.6 (low pH tester; 7.6 is the maximum on low tester)

    API 5 in 1 Test Strips (newly purchase)
    -Nitrite: 0.5
    -Nitrate: 20
    -pH: 7
    -KH: 40
    -GH: 30

    Pet Store Test (Test strips used by aquarium staff)
    -Nitrite: 0-0.5 (~0.3)
    -Nitrate: 20
    -KH: 60-80
    -GH: 75
    -pH: 7-7.2

    What do you think of the diffeing test results? How come pH is completely off for my home liquud test? I always thought liquid would be more accurate.

    Ignoring the pH, I added Prime, 16oz baking soda and 2 pounds of epsom tonight. Will retest tomorrow evening before taking further action

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