Backyard Aquaponics
A place to discuss aquaponics

The deformed tail could be because of an electricity leak. I've had a similar problem with some of my orfe that got deformed tails and swimming bladder problems - I think it was from electricity. The bigger koi fish were fine though, and I didn't have any problems with them losing scales.

But it could be parasites, too, or toxins. In those cases, you should do frequent water changes which you're already doing.

I don't think it's a deficiency; koi are very strong and the problem seems to be more short-term.


What kind of water do you fill the pond with? Is there any chlorine in it?
I used to use chlorinated tap water to fill my pond and had frequent fish deaths. I haven't had any fish deaths since I stopped using tap water. Could be because only the strongest survived though?


Just a thought; the "good quality" koi are actually the inbred ones that show a certain colour pattern. If you don't hand-pick them for that, they'll become brown and very much like wild (hardy) carp after only one or two generations.

Not sure what actually went wrong, but there are now two remaining kois... they are coincidentally the bigger ones, although there were big ones in the initial series of deaths as well...

Well I do use chlorinated tap water to top up the tank but I doubt it is the chlorine affecting them. I think it is probably a series of issues that caused the fish death, starting with high water temperatures, parasites and so on...

I guess the remaining 2 kois may be built strong...