folded fin on koi

[legendaryhound]

My butterfly koi has been swimming around with the dorsal fin folded more than not. I'm a very newbie to koi and I grew this one from a small retail store fish to his current size, about 4 inches. I didn't even know it was a butterfly koi till I began to search. There is also a calico fantail (Minion) who I grew a year in a small container garden before I brought them inside.
I'd like to know what's ailing the koi (Lackey) before it has gone on too long to fix.
Thanks to all for any guidance you might give.

 

[jlk]

Welcome to AA!!!

Can you please provide us with some more information? Is this fish in a pond or tank? Size? Parameters? Water change schedule? Stocking? How long have you had him exactly? Thanks!

 

[legendaryhound]

More information

The butterfly koi is in a 20 gallon tank with one other fish, a smaller calico fantail. I believe I have had them 2.5 years. They spent their first summer in a container water garden outside. This is their second summer inside, and they have been upgraded from a 10 to a 20 gallon tank because they grew so much and my water got cloudy. I use a Topfin 20 filter.
I do not have a water change schedule......I don't know any better but have been reading and now realize I must do that. I have set water out to condition overnight and will replace some water tomorrow.
As you can see I'm not a very sophisticated fish owner. As a child we had goldfish and tropical fish in simple set-ups but I have not kept fish in years. There have been lots of changes since I was young.
Thanks for your interest and I hope this information helps. I'm learning....

 

[Jmunroe]

Tank is extremely to small for a koi. And no water changes it is probably very stunted. I can't believe it is still alive to be honest. You need a large tank or better a large pond.

 

[brunettebaby4571]

Are you using any water conditioner in the water you are setting out overnight? It won't simply "condition" just by leaving it sit overnight. You will need to add some water conditioner to remove chlorine, chloramines, and other stuff in the water. A lot of people recommend Seachem Prime but there are many others you can use as well. Just simply add the recommended dose to the new water and then you can add it straight away to the tank. Also as already mentioned you will definitely need to upgrade to a much much larger tank or pond for koi and goldfish. But for the time being you will definitely need to be doing lots of water changes for these guys!