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




About the Author:


  1. 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.

  2. 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.

  3. 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

  4. 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

  5. emme July 16, 2017 at 3:35 pm

    Pond water stats this morning:
    Ammonia: 0.1
    Nitrite: 0.3 (it’s increasing)!
    Nitrate 5-10
    pH: 8.4-8.6 (color in between)
    KH: 40
    GH: 60
    Salinity 0.09

    I know I messed up the baking soda, but given the high pH, I’m very worried adding more to raise KH will cause the alkalinity to be off the charts (tester cannot read past 8.6). What do you suggest?

    Should I add more Epsom? How much?

    Also, what can we do about the bacteria/fungus in the pond?


  6. Venus July 16, 2017 at 8:54 am

    Do you know the depth of the pond?

  7. emme July 15, 2017 at 7:13 pm

    I just added 2 pounds (900gm) of Epsom salt and 16oz (500gm) of baking soda. Also added Prime. Will test pond water tomorrow!

    • emme July 16, 2017 at 3:24 pm

      Hi Brenda,

      Wow last night was a roller coaster. The diseased fish died so we took it out of the pond. It took the effort of my brother and I to fish it out with a big net. And of course now we’re worried about how long the fish was in the pond for and whether the bacteria or parts of its remains were eaten by other fish. We have observed finrot, some white patches and some injured, raised white scales on fish though.

      I took the pond parameters last night and they were
      PH 8.6
      KH is 130
      Ammonia 0.1
      Nitrite 0.1-0.3
      Nitrate 5-10
      GH 80
      Salinity 0.11

      I was shocked about the KH, thinking the sudden high pH and KH would stress the fish. Out of panic I removed 20gallons of pond water and added new tap water.
      I remeasured the pond parameters but due to the slow water mixing, I decided to wait to remeasure this morning

  8. Venus July 15, 2017 at 1:02 pm

    Epsom is pure magnesium, and won’t raise or lower salinity levels. Soda will raise the levels, but insignificantly. Once KH is in the comfort zone, the fish will have the precise amount of salt they need from the carbonate mineral.

    The soda is going to raise pH, but only slightly, as the KH levels are still way too low. I would guess it’s the combination of raising KH and adding water to the pond. Freshwater is loaded with oxygen

    Keep this in mind; this pond is a monster, and it’s going to take time for the substances we’re adding to mix up well with the water. The same is true with the salt that’s been added. There may be areas of the pond that have more salt than others. From the photo of the overall pond, I was a little concerned that the water wasn’t agitated enough, but with your KH being so low, and your pH being over 7. I thought it wouldn’t be an issue. Still think it’s going to be fine

    It’s critical to raise GH and KH. Let’s keep adding Espom until levels are at the bottom or middle of comfort zone; 200 to 400 ppm

    Let’s stop adding soda when levels reach 80 to 100 ppm, and once the salt isn’t as issue, we’ll raise to 100 to 120 ppm. This way we won’t be pushing salt levels too much. Salt or no salt in the water, the KH levels are critical

    KH gives water the ability to support oxygen. It may have a little salt, but salt is also vital to animal life. Keep up the good work

    If you’re of the mindset. Pick up a dozen boxes of organic peppermint or spearmint tea, and let us know when and if you do. I was thinking a mint treatment may be in order

  9. Venus July 15, 2017 at 6:39 am

    Glad they liked the peas. Peas are really nutritious and high in roughage

    Did we really go from .09 to .01 in salinity? That’s amazing, and a big relief

    The ammonia and nitrite reading; is it .1 or 1. just to be sure, as .1 is insignificant, but still enough to treat with a a half dose. I would also like to get you into the habit of treating your freshwater. Water treatment is supposed to be premixed in freshwater before adding, but with a pond of this size it’s difficult to do, and because you’re topping off so frequently, I think it would suffice to treat the pond, and then run the hose

    Just so you know; most large pond keepers would run water into a 55 gallon drum, add water treatment, and then siphon the water into the pond with a hose. Some rig the drum with an opening for a hose at the bottom, and some don’t every bother to treat the water at all with no ill effects. That’s the beauty of a large pond. It’s rare that water changes are performed

    You got the Prime water treatment; right? How often are you topping off? Add a single dose every time you top off until ammonia and nitrite recede

    To add water treatment, break up the amount you’re going to add to the pond into three parts. Add one part at a time to a two or three gallons of pond water. Walk around the pond slowly adding the treatment, mixing with a broom

    Add another two pound bag of Epsom and two 16 oz boxes of soda or half a four pound box; might as well. It looks like we’re going to need it. It’s going to take some doing

    Good news is; the ammonia and nitrite is not rising; it’s on it’s way down. If you could possibly find out if your city is using chloramines or not, this well help us determine if we’ll need to continue using water treatment when water is added to the pond. Chlorine is a liquid gas, and soon evaporates in moving water, but chloramines has ammonia in it. I’m thinking there’s a very good chance you don’t have chloramines. Most folks get a .25 up to .1 reading in their freshwater for ammonia. Chloramines is combined ammonia (combined with chlorine)

    We’ll wait another day after adding the soda and Epsom, giving plenty of time for an accurate result. Better to move slowly so as not to go over

    • emme July 15, 2017 at 11:44 am

      Hi Venus,

      The salinity level increased from 0.09 to 0.1 after I added the 2 pound of Epsom salt. It will probably increase again after I add another 2 pounds today.
      Ammonia and Nitrite are definitely 0.1 (lowest-second lowest color on the chart), I think it was remained the same, no change.
      I am topping water daily with the garden hose for about 2 hours each day. That only raises the pond water level by about 2 inches overall.
      I will add another 2pounds of Epsom tonight. I’m a bit concerned about the baking soda though, because the pH moved from 7.4 to 8 in one day. Can I add 8oz for now?
      I will start adding Prime tonight too – enough prime to treat just the water being topped off and divided into thirds mixed with pond water.

  10. emme July 14, 2017 at 11:23 pm

    Hi Venus,

    I fed the fish peas today (full and unmushed) and they all seemed to like them. I think the size/look of the food matters as the peas kind of resemble their pellets.

    I also tested the pond water parameters:
    Ammonia: 0.1
    Nitrite: 0.1
    Nitrate: 5-10
    pH: 8
    KH: 20
    GH: 80
    Salinity: 0.1

    Should we add Prime or more Epsom salt/baking soda? How much?
    I’ve added 2pounds of Epsom and 16oz of baking soda so far

Leave A Comment

Skip to toolbar
View My Stats