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. 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

  2. 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!

  3. 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

  4. 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

  5. Venus July 17, 2017 at 4:05 pm

    It seems we’re having problems with the comments loading in their proper order after deactivating the load comments button, but I’ll try to keep watch over it, and make sure you’re seeing my post.

    Yes, you got it with the Prime. And we wondered why we were forced to take math in school. lol

    Raising the KH is going to kill the bad bugs in the water. Bad bugs can’t tolerate water high in alkalinity; rich in oxygen. That in itself is all the treatment you need. That being said, in order to hasten their healing, other treatments are recommended. Treatments that won’t disturb the already delicate cycle; hence the garlic remedy. If you want to add some mint tea; that would be great, as mint also destroys bad bugs; still, we should wait until the KH is where we want it before adding any remedies

    You should receive the garlic in a day or two, and by then the water should be rich in carbonate mineral.

    Yes to the Espom and the soda

    If we don’t see a large boost in GH after adding the Epsom, it’s possible you have low calcium levels. If you are of the mindset, contact your parents water department. Ask what calcium, magnesium and carbonate mineral levels are. Hopefully, they can provide the info. I looked online, and can’t find any info on substances in your water.

  6. Venus July 17, 2017 at 10:43 am

    It’s disappointing to see nitrites on the rise, but you’re armed with water treatment. The ammonia is stable with nitrites on the rise, meaning you’re a little more than halfway through the cycle. Nitrite should peak at 8. ppm, and then recede a short time after. Due to the fact you have nitrates, the cycle isn’t broken; a portion of the colony was lost, and now they’re rebuilding

    The water loss is going to be very helpful with this. Adding fresh water will take the place of the usual water change, diluting the toxin levels

    Double dose of Prime today by adding dividing each dose in half; diluting in a bucket of pond water. Pour all around slowly mixing with your broom. You got that by now, so I won’t repeat it. So this means two doses each split in half; four buckets total

    As nitrite rises, the dosage will increase up to four doses daily. Once the levels begin to recede will back off to every other day, lowering the doses

    Don’t worry about pH, just keep working on increasing the KH; it’s all important

    By the way, did I recommend H202? If so, that would account for the high pH, but if not, let’s just not worry about pH right now. We can rest assured oxygen isn’t an issue anyway.

    • emme July 17, 2017 at 12:10 pm

      Hi Venus,

      Should I add 16oz baking soda and 2pounds of Epsom again today?

      I have been following the bottle directions of 5mL Prime for every 50gallons of fresh water added so far. If I double the dose, then I would be adding 10mL Prime for every 50gallons of fresh water added, yes? Just to confirm though, say I top up 1000gallons of water each day (about 2% of the pond total of 50,000 gallons, to be conservative), then the normal dose of Prime to add daily would be 100mL. By doubling the dose of Prime, you are asking me to add 200mL of Prime each day (divided into 4 buckets) to each 1000gallons of new water.

      No, we haven’t used hydrogen peroxide so far. But do you recommend we do anything about the bacteria/fungus in the pond? Some fish have visible white patches on their bodies.

  7. Venus July 16, 2017 at 4:00 pm

    Something’s off with the pH or the KH test. Maybe you’re using a high pH test kit? It’s impossible to have KH at 40 and pH over 8. Take a sample of your tap and pond water to the pet shop for a free KH test; ask for specific readings. We need to know for sure that 40 is what you’re pond is reading. I have a feeling it’s right, and pH is off, because of the condition of the pond

    Or…pick up another KH test kit so we can double check ourselves

    We need to know for sure before we proceed

    • emme July 16, 2017 at 7:13 pm

      I added more tap water today to top off the pond. I tested KH and pH twice.
      KH is currently 20
      PH is currently 7.8-8

  8. Venus July 16, 2017 at 3:42 pm

    Sorry to hear you lost that fish, but it was pretty much eaten up. You don’t have to worry about the spread of infection now that the KH is up. It’s a little high, but you may have tested a pocket, and it’s not too high; so no worries there.

    As long as the KH is comfortable, we don’t have to worry about pH, but we do know the pond is heavily oxygenated, and that’s pretty awesome. Stress is caused by low KH and pH, not by raising it

    Also wanted you to know that the test kits we buy at the pet shop are pretty cheap compared to the what the pros use. Because of it, we don’t always get accurate results. Our KH kits test 20 ppm to 30 ppm lower than the actual readings, so you’re probably just where you need to be

    Salinity looks fine too

    Need to keep working on GH. This is important as well. Keep a close watch on the KH, because it’s going to drop; this is natural when buffering and adding freshwater. When it drops to 80 ppm, add a few ounces of soda. It’s hard to believe it, but by the time your parents come home, you’ll be a pro, and then you can teach them. It’s not really that hard now is it?

    I think it’s important to wait at least 24 hrs in between or before adding more substances. Meaning; wait 24 hrs after buffering to test and buffer again. If you test in the morning, and find GH is still at 80; add 4 lbs of Epsom

    Check with your parents and see if they know if the house is on a filtering system. I would be so. If this is the case, you may be able to have someone re-route the hose. You can also contact your city water department for KH and GH levels. Most of these people can test for you if they don’t know. This could determine if it would be worth the effort to re-route the hose from the filtering system, or, we may find out there’s no filtering system at all, and your water is low in mineral value

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