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 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?


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

    Do you know the depth of the pond?

  3. 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

  4. 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

  5. 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.

  6. 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

  7. Venus July 14, 2017 at 5:49 pm

    Oh, okay. I was all excited to see zero ammonia and nitrites, but we may be surprised anyway, and it’s good to know these toxins aren’t present in your tap. Some aren’t as fortunate.

    Let’s wait to see ammonia and nitrite readings until we determine Prime usage

    Open it up, and pull as much gunk away as possible. If they’re any filter pads or sponges, rinse them clean in a bucket of pond water. Toss the water of course. If the water is moving from the hoses, it’s doing it’s job; don’t bother if this is the case

    • emme July 14, 2017 at 11:25 pm

      Hi Venus,

      What do you mean by water moving from hoses??

  8. emme July 14, 2017 at 3:32 pm

    Hi Venus,

    I just wanted to clarify that the water parameters I posted were those of the fresh water that came out of the tap, not water from the pond. I haven’t tested the pond water since I added the Epsom and baking soda but will do so tonight!
    Would the amount of Prime I add depend on the readings?

    Also, my parents gave me no directions on how to clean the filtration system while they are away. Is there a correct way to clean the filter/collected pond debris and how often?

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