Mysterious Koi Death

[Fishpony]

Hello everyone!
Today one of my ~10 inch koi recently died to an unknown cause. All the other koi are doing fine and eating with vigor. This koi was doing perfect yesterday and was eating well, but when i found it dead on one side of the body it was almost descaled, while the other side was fine. The fins were also tattered to some extent.
My stocklist
5-6 large koi
2 Large common plecos
1 Ripsaw catfish
2 Small oscars
I think it was a common pleco who wanted his slime coat.

Edit: I netted out my two plecos to check if they were underfed, they weren't thin but weren't fat either.
I looked at the other koi as well and they had no lost scales either.

 

[dcorreia]

Did you check your water levels? I had 2 koi die last year that I'd had for almost 8 years. The ammonia levels had spiked in my pond and I didn't realize it. Also, maybe the other fish picked the scales off him once he was dead, koi do that sometimes. I'd start with checking your levels.

 

[FishPondSealant]

Sorry for your lost Fishpony , hope all others will remain safe and sound. If there is Pond/tank problem then pondpro2000 is the best solution I recommend. Thanks

 

[Lorraine41]

Anyway if doing a scrape? To get a sample under a microscope to check for parasites.

 

[MrsE88]

Do you have an idea how long it may have been dead for?
The missing scales could easily be from any of the others taking advantage of a free meal after it died.
What has your water tested at?
Any pictures by chance?