5 large Koi have died in the last 3 months

[parabous]

I'm looking for advice to stop my collection from shrinking further after losing five large Koi in the last 3 months, including a 50cm beauty.

Background: I emptied and rebuilt my pond about 6 months ago and used bore water to fill it (with a ph of 7.8), which has remained steady throughout. I introduced 5 new fish around 3 months ago and have since lost a few of them, along with some of my original collection.

I've checked the ph, ammonia, iron levels, and the temperature is also stable and no higher than it was a year ago when I acquired many of the fish. I have a fountain, good filtration, and the water is relatively clear.

Where should I go from here? I'm considering quarantining the remaining new fish. What else should I focus on?

A link to a recent video:

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[Lisak1]

All you had to say was "I added new fish" - that's your answer right there. You introduced something into your herd that has contaminated the lot. Did you quarantine before you added them?

Basics please - how big is your pond? How many fish do you have and what type/size? What types of filtration are you using? (More info than "good" please). Do you test your water? What are the exact numbers? Do the fish show any signs of illness before or after they die?

 

[Lisak1]

Let me add - few here will be willing to download your video. Its best to upload to Youtube and share the link here.

 

[WaterGardener]

Sorry you are losing fish. As @Lisak1 said, the problem was likely introduced with the new fish. We really need the information she requested to try to help you and your fish.

We have all made mistakes that our fish have had to pay for. At this point we just want to help and prevent more problems. We just need more information.

 

[Mmathis]

How big is your pond?

 

[GBBUDD]

I would avoid in practice any major changes close to one an other. Rebuilding a pond is definitely a stressful time for your fish. The biggest issue with fish is stress they / koi in particular are not a indestructible breed.

The more stress the more susceptible they are to disease. The slime on their body is that immune system.
I agree adding fish could be the main issue even of guaranteed was done. I would get so.e serious air going in your pond and start prazzi and proforma c regiments to knock down what ever it may be but you better do it fast as temps are dropping and ifbyour already at 50 its too late.

 

[parabous]

No signs of anything before they die other than maybe isolating themselves in the 24hrs before they die. Another today!

I didn't quaratine the new fish, I now have about 15 left, all Koi (10 x avg 25cm) or large Comets (5 x avg 18cm).

PH: 7.8
Ammonia was fine, at the lowest level on the colour indicator.
Iron, same as ammonia, lowest level on colour spectrum on the tester I used.

100k litres of water.

Filter: OASE BioTec ScreenMatic² 140000

Fountain/aeration:

Do I need to get these fish out, do I need antibiotics? Do I need them individually contained? I'm in a panic as I'm losing one a week.

 

[parabous]

This morning:

 

[parabous]

The day before this one died

 

[parabous]

My 50cm

 

[WaterGardener]

It's too late to get those fish out. All your fish have been exposed and, sorry to say, that isn't reversible.

What about the nitrite level?

Do you have a test for KH? If the KH tests as adequate, anything 100 or better, and the nitrite is zero, then I would treat the pond. If those are not at the safe levels they should be addressed and corrected.

If the water parameters test as desired, I would do as @GBBUDD suggested and treat with Proform C or another product with the same ingredients, malachite green and formalin. That's a 3 day treatment. On the third day I would include a medication for flukes, Praziquantil or Fluke-M. I find that Fluke-M is the more effective choice.

Those medications will not kill your beneficial bacteria so there is no problem with interrupting the nitrogen cycle.

 

[parabous]

 

[parabous]

Is that KH a concern? Remember that PH is 7.8 on a calibrated digital tester.

 

[WaterGardener]

I think the KH is fine. Many koi keepers like to see it at 200 or so, and mine has gone over 300 before with no ill effects to the fish. Excessively high KH can possibly cause the pH to get too high, but you aren't having that problem.

KH will fall over time as it neutralizes the acid being produced by the fish and by the nitrogen cycle itself, so it should be checked now and then to prevent it from getting too low.

 

[GBBUDD]

I have not seen that test kit color chart before are you using strips? If so get liquid.

No quarantine, I would be doing those two treatments regardless. I would also do a bacterial treatment. Though I see no signs now with winter coming it will be too late if temps get below 50