All big 10-12 inch koi died with a week

[Frisco]

Within a week all the big koi (10-12") died in my pond inside a screened patio. No bumps or sores on them. No bloating. Just floating dead.
Started feeding new food 2-3 weeks prior but no recalls found. Water tests seem fine. Smaller koi and comets are still fine.
Had the fish about 2 years.
Any ideas as to cause?

 

[mrsclem]

I'm thinking because it was the larger koi that it's an oxygen issue. Can you give us more info about your pond? Gallons, number of fish and sizes, any chemicals added and your actual test results. What tests did you do, what type of test kit and actual numbers.
So sorry for the loss of your fish but lets see if we can figure out why it happened.

 

[Lisak1]

I'll second @mrsclem - when it's the big fish that die the first thing you suspect is low oxygen. Details will definitely help.

 

[addy1]

Welcome to our forum!

What size is your pond? About how many fish do you have in it? Where are you located, warm or cold.

 

[JamieB]

I agree. Bigger fish tend to require more oxygen, where if it was a food/ water quality/ illness, it would most likely be a mix of sizes.

 

[Mmathis]

Hello and welcome! So sorry to hear about this! I tend to agree with what the others about possible cause of death — it might be an oxygen issue. Doubt that it’s the food.

Please give us some information about your pond. The more information we have to go on, the better.

• How big is your pond — gallons, dimensions?
• how many fish, total?
• what are the actual numbers for your water tests? “Water tests seem fine “ isn’t enough information
• what kind of filtration?
• Do you have a waterfall and/or any type of aeration?
• Where do you live?
• have you added any new fish recently?
• how often do you feed?
• is there any yard water run off that gets into the pond?

 

[j.w]

@Frisco
I too think something is happening w/oxygen for the bigger fish. My neighbor had a paint overspray from a project near his pond and it killed all his koi.